sctpassociation: check usrsctp_finish's return code.
sctpassociation: check usrsctp_finish's return code.

And only call usrsctp_init() again if finish succeeded.

There are cases where finish may fail, and calling init again
afterwards causes various race conditions.

usrsctp's example programs check for the return code
(see
https://github.com/sctplab/usrsctp/blob/0c44eac/programs/client.c#L273),
calling sleep(1) as long as the call didn't succeed.

I don't think this an option here, and maybe some more complex logic
could be implemented using a timeout, but the goal here is simply not
to trigger the error conditions that may arise from calling
init again after finish failed.

Closes #56.

EricssonResearch/openwebrtc-gst-plugins,EricssonResearch/openwebrtc-gst-plugins,EricssonResearch/openwebrtc-gst-plugins,sancane/openwebrtc-gst-plugins,sancane/openwebrtc-gst-plugins,sancane/openwebrtc-gst-plugins