RTP dynamic bitrate depending on network condition

[Marc Leeman]

FYI, you are not using RTP in that pipeline; simply payloading the
data in RTP format. If you do not link up your RTCP socket/rtpbin your
quality will be poor in less than ideal network conditions.

See:
https://github.com/mleeman/gst-plugins-rtp

Also (I still need to revert the boilerplate)
https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/merge_requests/183