Changes

TW-TS-* support: pass RTP extensions to MGW

As of 2025-03-10 (I0d58e6d84418f50670c8ab7cf8490af3bc2f5c26 merge)
OsmoMGW supports an SDP extension that enables the use of TW-TS-001
and TW-TS-002 enhanced RTP formats for FR/EFR and HRv1, respectively;
libosmo-mgcp-client likewise supports a mechanism to request these
extensions.  At the present time OsmoMGW rtpbridge endpoints don't
do anything different when these extensions are enabled (they
originate from OsmoBTS in this case), but for E1 Abis endpoints
the new MGCP extension controls whether or not these MGW endpoints
emit the enhanced RTP formats in question.

Changes to OsmoBSC:

1) Allow TW-TS-001 and TW-TS-002 to be enabled on all E1 BTS -
   previously not allowed.

2) Whether E1-based or IP-based BTS are used, when RTP extensions
   have been enabled by CN request (BSSMAP IE of TW-TS-003),
   pass them to the MGW endpoint controlled by this BSC.

The second change makes RTP extensions work on E1 BTS, and also
paves the way for future OsmoMGW rtpbridge improvements where
the MGW might do additional processing that needs to be disabled
when TW-TS-* extensions are in use.

Depends: osmo-mgw.git I0d58e6d84418f50670c8ab7cf8490af3bc2f5c26
Change-Id: Iaa6e4c56313f06b79852c06dcec686f21950e638