* re-introduce ST_ONSET_F to guard from repetitive ONSET messages in case
multiple FACCH occur duriing DTX silence period.
* produce ONSET event after both SID FIRST and UPDATE in case of AMR FR.
* always dispatch E_SID_F (SID FIRST) signal if in talkspurt.
* allow E_SID_* right after ONSET (zero-length talkspurt).
* add missing E_ONSET signal description.
* fix FSM transitions for AMR HR *Inhibited and First P*.
* fix incorrect return from l1if_tch_encode() in ONSET FACCH with
incoming SID UPDATE
Change-Id: I0e9033c5f169da46aed9a0d1295faff489778dcf
Related: OS#1801