gscon: use BSS-common payload types on BSS side

In cases where a codec has no fixed (IANA) payload type number, a
dynamically coosen payload type number is used. For the route between
BSC and MSC 3GPP as designated certain payload type numbers. However,
beond that, those payload type numbers may not necessarly apply. The
RTP communication between BTS and BSC still might run on a completely
different payload type number.

libosmo-netif contains a header file which payload type numbers
shall be used. Lets use those in order to signal the same payload type
numbers as we actually use in the RTP packets to the MGW.

Change-Id: I507a1b1446c8f140b2950d73cf737797604c1ac3
Related: OS#2728
Related: OS#3384
5 files changed