sdp get/write refactoring; SSRC->Ssrc
sdp get/write refactoring; SSRC->Ssrc

Acidburn0zzz/adapter,jan-ivar/adapter,xdumaine/adapter,webrtc/adapter,Acidburn0zzz/adapter,Acidburn0zzz/adapter,xdumaine/adapter,jan-ivar/adapter,webrtc/adapter