Make RTP payload type configurable

For a long time the RTP payload type was hard-coded for outgoing
frames. The problem is that according to RFC 3551 only GSM FR has
a static payload type value (see table 4, value 3). For other
codecs the payload type may be negotiated between the both
sides dynamically (i.e. in range 96-127).

Let's allow a binary/API user to configure this manually.

Change-Id: Ia07ed4e13b4a70c8bb4181564a8190861fd269da
Closes: OS#2482
4 files changed