Integrate webrtc stream addition/removal

[jdm]

https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/merge_requests/167 is a recent merge requrest for gstreamer. It looks like something we might care about, and will require changes to gstreamer-rs before we can make use of them.

[sdroege]

will require changes to gstreamer-rs before we can make use of them.

For gst_webrtc_rtp_transceiver_set_direction() you mean? As a workaround you could also call that directly, but I'll add it to the bindings together with the 1.16 GStreamer release :)