webrtc-api: Set default bundle policy to max-bundle

Otherwise the default is "balanced" and GstWebRTC-based browser engines don't
support this very well. Max bundle is already un-conditionally enabled by
default in webrtcsink.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/2352>

net/webrtc/gstwebrtc-api/src/config.js

@@ -47,7 +47,8 @@ const defaultConfig = Object.freeze({
           "stun:stun1.l.google.com:19302"
         ]
       }
-    ]
+    ],
+    bundlePolicy: "max-bundle"
   }
 });