Allow dynamic RTP payload types when bridging between SIP and OpenBSC.

Allow dynamic RTP payload types when bridging between SIP and OpenBSC.

Because EFR/AMR/HR codecs use dynamic RTP payload types, it is essential
to forward the actual media types between endpoints too. These media
types are used for negotiation of codecs. A dynamic payload type is
used as given by remote peer. Locally generated payload types are used
when offering codecs to remote peer.