Changes

trau/clearmode.h: add OSMO_CLEARMODE_20MS definition

RFC4040_RTP_PLEN was previously defined privately in OsmoBTS and
in trau_rtp_conv.c module in this library, but there was no official
definition in any of Osmocom headers.  Add <osmocom/trau/clearmode.h>
header with OSMO_CLEARMODE_20MS definition.

Change-Id: I4b2e49b085574336820468dc8cfb8e32377788bf

trau: factor out V.110 frame conversion functions

Implementation of CSD conversion between TRAU frames and CLEARMODE
inside osmo_trau2rtp() and osmo_rtp2trau() contains lower-level
functions for conversion of individual V.110 frames and for alignment
checking.  Factor these functions out into API, as they are useful
for other applications besides TRAU<->RTP conversion:

* Compression and decompression functions that convert between
  standard (but inefficient) CLEARMODE and compressed-CSD RTP format
  of TW-TS-007;

* Implementations of IWFs that terminate CSD RTP streams at the CN
  and support both CLEARMODE and TW-TS-007.

Change-Id: I3f51254b4b985a0f8499c375b61069ca24f77ae8

trau_rtp_conv: use factored-out V.110 functions

In the previous patch we factored out V.110 frame conversion functions
into API.  Now use these new API functions in the implementation of
osmo_trau2rtp() and osmo_rtp2trau().

Change-Id: I375311ff9be1b10d27ac94e2e9bd227e7241e7f0

trau: add TW-TS-007 packing and unpacking functions

TW-TS-007 packing and unpacking functions in <osmocom/trau/twts007.h>
are symmetric, as much as feasible, with their CLEARMODE counterparts
in <osmocom/trau/csd_v110.h>, <osmocom/trau/csd_ra2.h> and
<osmocom/trau/csd_raa_prime.h>.  This symmetry is intended to aid
implementation of CSD RTP endpoints (TRAU<->RTP functions and IWFs
in the CN) that support both payload formats, and it will also serve
as a building block for dedicated format conversion functions.

Change-Id: Ie81280d2b90f69fbdde9fa968f747a35ea123f79

trau: add TW-TS-007 compression and decompression functions

These are high-level functions that convert a CSD RTP payload
between CLEARMODE and TW-TS-007 formats.

Change-Id: I10a86f5e4a7323cf06fb1d2624757c34bd23218f

rtp2trau CSD: accept both CLEARMODE and TW-TS-007 payloads

Change-Id: Ide89de89ed43df5762a091f1577a8b8e84b55738

trau2rtp CSD: add option to emit TW-TS-007 payloads

Setting OSMO_RTP_EXT_TWTS007 bit in st->rtp_extensions switches
CSD RTP output format from standard but inefficient CLEARMODE to
the compressed-CSD RTP payload format of TW-TS-007.  This new
mechanism is fully symmetric with already implemented mechanism
that enables or disables TW-TS-001 and TW-TS-002 RTP output
for FR/HR/EFR speech codecs.

Depends: I2cc2c9340f9fa5c7111447a6beef49c335fa1107 (libosmocore)
Change-Id: I86d628c65104a119ef0fb9f27f5835c9a1769971