ts-jitterbuffer: set jbuf delay when instantiating it

The internal (C) jitterbuffer needs to know about the configured
latency when calculating a PTS, as it otherwise may consider that
the packet is too late, trigger a resync and cause the element to
discard the packet altogether.

I could not identify when this was broken, but the net effect was
that in the current state, ts-jitterbuffer was discarding up to
half of all the incoming packets.

generic/threadshare/src/jitterbuffer/imp.rs

@@ -1080,7 +1080,12 @@ impl TaskImpl for JitterBufferTask {
             self.sink_pad_handler.clear();
 
             let jb = self.element.imp();
-            *jb.state.lock().unwrap() = State::default();
+
+            let latency = jb.settings.lock().unwrap().latency;
+            let state = State::default();
+
+            state.jbuf.borrow().set_delay(latency);
+            *jb.state.lock().unwrap() = state;
 
             gst_log!(CAT, obj: &self.element, "Task started");
             Ok(())