Changes

trau: new function osmo_trau2rtp_ufe()

TRAU frame formats for newer codecs (HR, EFR, AMR) include a UFE
(uplink frame error) indicator bit in the DL direction.  TRAUs are
expected to set this bit to active error state (0 for HR/EFR/AMR or
1 for D144 E-TRAU) if frame synchronization is lost in the UL
direction, or if received TRAU-UL frames have bad CRC or invalid
control bits - errors that indicate corruption on terrestrial
circuits or faults in the CCU, rather than radio Rx errors.

In Osmocom implementation, TRAU frame CRC and control bit patterns
are checked during conversion to RTP, as part of the work done by
osmo_trau2rtp() - but there is no separate return indication from
that function that distinguishes these errors from ordinary BFIs
due to radio errors or FACCH stealing etc.  Solution: add a new
API function that indicates UFE conditions separately.

Related: OS#6614
Change-Id: I7a90eca296b17b1211e5c2125fb1496cd362e1c9