Allow to change the stream type if the port is
SAL_STREAM_DESCRIPTION_PORT_TO_BE_DETERMINED (i.e. 65536).
Do not create a media description upon reception of an INVITE message if the offer will be in the 200Ok response. This will prevent the following:
- create an SDP before knowing the actual call parameters to be used in the call (they are set by MediaSession::accept())
- start an ICE gathering with a media description that may not be the one that will be put down in the 200Ok response