Max authored Oct 26, 2016 and Harald Welte committed Oct 28, 2016

Handle ONSET cause by Voice and FACCH separately. In case of Voice we
have RTP payload which we have to cache and send later on in next
response to L1 RTS. FACCH have higher priority so it preempts both voice
and silence alike - hence we can send ONSET immediately but still have
to track previous state in order to get back to it gracefully.

This affects lc15 and sysmo hw as there's no FSM-based DTX
implementation for other models yet.

Note: this requires patch for OpenBSC which adds FACCH buffer to tch.dtx
struct.

Change-Id: Idba14dcd0cb12cd7aee86391fcc152c49fcd7052
Related: OS#1802