Use our own SSRC when sending packets on the RTP control stream

This solves a streaming issue when using RTP/Unicast streaming with AXIS encoders.
ZM reuses server SSRC as client SSRC and this generates conflicts.
 
All credits to libav for the fix:
https://github.com/libav/libav/commit/952139a3226b4668bfa1e523599a5fe89592de0c
https://github.com/libav/libav/commit/ad7beb2cac1563e87171a4d044a6d526527d81d9