webrtcsrc: Fix caps used when creating transceiver

We used to pass all media keys and attributes to the caps which
incorrect. Instead we should be using only the keys from the map
and remove all information related to rtcp which is irrelevant
to create the transceiver.

This also simplifies the code.

New caps look like:

```
Caps(
    application/x-rtp(memory:SystemMemory) {
        media: (gchararray) "video",
        payload: (gint) 96,
        clock-rate: (gint) 90000,
        encoding-name: (gchararray) "VP8",
    },
    application/x-rtp(memory:SystemMemory) {
        media: (gchararray) "video",
        payload: (gint) 102,
        clock-rate: (gint) 90000,
        encoding-name: (gchararray) "H264",
        packetization-mode: (gchararray) "1",
        profile: (gchararray) "baseline",
    },
    application/x-rtp(memory:SystemMemory) {
        media: (gchararray) "video",
        payload: (gint) 104,
        clock-rate: (gint) 90000,
        encoding-name: (gchararray) "H264",
        packetization-mode: (gchararray) "0",
        profile: (gchararray) "baseline",
    },
    application/x-rtp(memory:SystemMemory) {
        media: (gchararray) "video",
        payload: (gint) 106,
        clock-rate: (gint) 90000,
        encoding-name: (gchararray) "H264",
        packetization-mode: (gchararray) "1",
        profile: (gchararray) "constrained-baseline",
    },
    application/x-rtp(memory:SystemMemory) {
        media: (gchararray) "video",
        payload: (gint) 108,
        clock-rate: (gint) 90000,
        encoding-name: (gchararray) "H264",
        packetization-mode: (gchararray) "0",
        profile: (gchararray) "constrained-baseline",
    },
    application/x-rtp(memory:SystemMemory) {
        media: (gchararray) "video",
        payload: (gint) 127,
        clock-rate: (gint) 90000,
        encoding-name: (gchararray) "H264",
        packetization-mode: (gchararray) "1",
        profile: (gchararray) "main",
    },
    application/x-rtp(memory:SystemMemory) {
        media: (gchararray) "video",
        payload: (gint) 39,
        clock-rate: (gint) 90000,
        encoding-name: (gchararray) "H264",
        packetization-mode: (gchararray) "0",
        profile: (gchararray) "main",
    },
    application/x-rtp(memory:SystemMemory) {
        media: (gchararray) "video",
        payload: (gint) 98,
        clock-rate: (gint) 90000,
        encoding-name: (gchararray) "VP9",
        profile-id: (gchararray) "0",
    },
    application/x-rtp(memory:SystemMemory) {
        media: (gchararray) "video",
        payload: (gint) 100,
        clock-rate: (gint) 90000,
        encoding-name: (gchararray) "VP9",
        profile-id: (gchararray) "2",
    },
)
```

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1216>

net/webrtc/src/webrtcsrc/imp.rs

@@ -9,6 +9,7 @@ use core::ops::Deref;
 use gst::glib;
 use gst::subclass::prelude::*;
 use once_cell::sync::Lazy;
+use std::collections::HashSet;
 use std::str::FromStr;
 use std::sync::atomic::AtomicBool;
 use std::sync::atomic::AtomicU16;
@@ -696,48 +697,39 @@ impl WebRTCSrc {
         let direction = gst_webrtc::WebRTCRTPTransceiverDirection::Recvonly;
         let webrtcbin = self.webrtcbin();
         for (i, media) in sdp.medias().enumerate() {
-            let all_caps_for_media = media
+            let codec_names = {
+                let settings = self.settings.lock().unwrap();
+                settings
+                    .video_codecs
+                    .iter()
+                    .chain(settings.audio_codecs.iter())
+                    .map(|codec| codec.name.clone())
+                    .collect::<HashSet<String>>()
+            };
+
+            let caps = media
                 .formats()
                 .filter_map(|format| {
                     format.parse::<i32>().ok().and_then(|pt| {
-                        let mut tmpcaps = media.caps_from_media(pt)?;
-                        {
-                            let tmpcaps = tmpcaps.get_mut().unwrap();
-
-                            tmpcaps
-                                .structure_mut(0)
-                                .unwrap()
-                                .set_name("application/x-rtp");
-
-                            if let Err(err) = media.attributes_to_caps(tmpcaps) {
-                                gst::error!(CAT, "Couldn't copy media attributes to caps: {err:?}")
-                            }
+                        let mediacaps = media.caps_from_media(pt)?;
+                        let s = mediacaps.structure(0).unwrap();
+                        if !codec_names.contains(s.get::<&str>("encoding-name").ok()?) {
+                            return None;
                         }
 
-                        Some(tmpcaps)
+                        let mut filtered_s = gst::Structure::new_empty("application/x-rtp");
+                        filtered_s.extend(s.iter().filter_map(|(key, value)| {
+                            if key.starts_with("rtcp-") {
+                                None
+                            } else {
+                                Some((key, value.to_owned()))
+                            }
+                        }));
+
+                        Some(filtered_s)
                     })
                 })
-                .collect::<Vec<gst::Caps>>();
-
-            let mut caps = gst::Caps::new_empty();
-            let settings = self.settings.lock().unwrap();
-            for codec in settings
-                .video_codecs
-                .iter()
-                .chain(settings.audio_codecs.iter())
-            {
-                for media_caps in &all_caps_for_media {
-                    let encoding_name = media_caps
-                        .structure(0)
-                        .unwrap()
-                        .get::<&str>("encoding-name")
-                        .unwrap();
-                    if encoding_name == codec.name {
-                        caps.get_mut().unwrap().append(media_caps.clone());
-                    }
-                }
-            }
-            drop(settings);
+                .collect::<gst::Caps>();
 
             if !caps.is_empty() {
                 let stream_id = self.get_stream_id(None, Some(i as u32)).unwrap();