osmo-trx: Avoid handling signals after shutdown triggered

Recently a blocked osmo-trx process was found after ending SIGTERM to
it.
Apparently one thread was handling SIGTERM and calling fprintf()
(grabbing libc lock) while another thread was handling another signal
and also grabbing similar lock. Both thread looked deadlocked there.
Probably this change doesn't fix the block on its own, but at least
simplifies scenarios inside signal ctx which can go wrong.

Change-Id: If91621913b8b03d8a0f4c863be0b0d479f97e8a1
1 file changed