fsm: add ignore_invalid_event_mask bit-mask

An invalid fsm event is an event which is not valid in the current fsm
state. Such invalid events will be logged and osmo_fsm_inst_dispatch()
return != 0. To prevent this log message which could be misleading for
the user, the code needed to add this event to the allstate_event_mask
or add it independent to each state. Or as alternative create a proxy
function in front of osmo_fsm_inst_dispatch() which checks the fsm state
before dispatching the signal. By using ignore_invalid_events the
logline can be ignored for certain events while for others the old
behaviour is still preserved.

Related: SYS#6145
Change-Id: Id010ade76de83ccf428f2d18e9f85bcce1d1ea2c
---
M include/osmocom/core/fsm.h
M src/fsm.c
2 files changed, 13 insertions(+), 0 deletions(-)