RTCP with RCE_SEND_ONLY and RCE_RECEIVE_ONLY flags

[jrsnen]

While RCE_SEND_ONLY and RCE_RECEIVE_ONLY work fine for RTP, the situation becomes more complicated when it comes to RTCP. When only sending, we should also have the local address and port so we can bind to it for receiving RTCP receiver reports. Similarly, the receiver does not know the sender address, so the remote address should be deduced from somewhere (check RFC 3550), probably sender reports so that receiver reports can be setn to the sender.