Changes

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