Changes

rtp2trau_hr16: set CRC bits correctly

The code previously failed to set the CRC bits in the TRAU frame
output, containing a misleading comment that this operation is done
by the TRAU frame encoding function (it isn't).  Set these bits
correctly in the rtp2trau step, like we do for EFR.

Change-Id: I5c8aa5891e3862f978f14093bff46bd00b6702a5

TRAU->RTP: add support for TW-TS-001 & TW-TS-002

The industry standard RTP payload formats of RFC 3551 and RFC 5993
drop valuable metadata from TRAU-UL frames of GSM 08.60 & 08.61,
and disallow transport of marked-bad frames.  Enhanced RTP transport
formats of TW-TS-001 (FR & EFR) and TW-TS-002 (HR) restore these
capabilities - however, because these formats are non-standard
outside of Osmocom+Themyscira GSM networks, their use can only be
optional.

Add rtp_extensions member to struct osmo_trau2rtp_state, specifying
the mask of RTP extensions to be used, just like we defined for
AoIP BSSMAP and Abis-IP RSL, and extend osmo_trau2rtp() to emit
these enhanced RTP formats when they are enabled.

Related: OS#6448
Depends: I0eccfe5ddcf44f8f20440acb01e2d4870ec0cd91 (libosmocore)
Change-Id: I7a6d13d406484c01210594bb6d2f0aff7c1341ab

trau2rtp_hr16: check CRC bits in the TRAU frame

If CRC bits in the received TRAU frame are bad, the implication is
that this frame must have got corrupted in E1 transport.  In this
case all other bits cannot be trusted, and we should deliver
BFI-no-data to RTP.

Change-Id: I4f97b67884ff7540be631298e5252d28f765fce9