Fixes an issue where the webrtcbin would hangup when finalizing due
to the sctpenc hanging up when finalizing. This occurred when the
webrtcbin chose to use a sctp association ID already in use.
The sctpenc would fail to reach the paused state, but startup a task
anyways that was never stopped.
This commit modifies the behavior to not choose sctp association IDs
randomly, and instead only choose one that is free. It also prevents the
sctpenc from starting up that task if it fails to reach the paused state.
Fixes: #4188
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8607>
If we don't receive any data from usrsctp, then there will be no src pad
for the stream id and the stream reset will fail to remove the relevant
src pad. Workaround by first attempting to add the relevant src pad, then
almost immediately removing it.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3381>
