gst-examples: no audio in webrtc sendrecv examples in certain configurations

The webrtc examples in gst-examples seem to be in a pretty bad shape:

• Fixed - webrtc-sendrecv --peer-id=7770 (C code) is crashing with ERROR:../subprojects/gst-plugins-bad/ext/webrtc/gstwebrtcbin.c:3188:sdp_media_from_transceiver: assertion failed: (trans->mline == -1 || trans->mline == media_idx)
• Fixed - sendrecv/gst-rust (Rust) called with --peer-id seems stuck in an loop where it keeps sending SDP offers.
• No audio - sendrecv/gst-rust (Rust) called without --peer-id works better, video streams work fine in both direction but audio is not received in the browser from GStreamer.
• No audio in webrtc-sendrecv --peer-id (C code) in GStreamer to browser direction

See also !3529 (merged)

I suppose those examples used to work so are those behavior changes in webrtcbin?