fix fallout from: 'stats: new trackers for lchan life duration'

In lchan_fsm_cleanup(), ensure that the time_cc timer is actually inactive
before deallocating. Do so via lchan_reset(), to also make sure the
timer is stopped in all other situations where the lchan is deactivated.

This fixes an infinite-loop deadlock as described in OS#5554:
- run BSC_Tests.TC_chan_act_ack_est_ind_noreply
- restart the BTS process after the test is done
- osmo-bsc enters infinite loop in osmo_timer_del()

The reason is that lchan_fsm_cleanup() fails to stop a running active_cc
timer upon lchan deallocation. TC_chan_act_ack_est_ind_noreply
incidentally terminates OML while the timer is still active.

Related: OS#5554
Change-Id: I901bb86a78d7d021c8efe751fd9d93e5956ac0e0

src/osmo-bsc/lchan_fsm.c

@@ -528,6 +528,14 @@ static void lchan_reset(struct gsm_lchan *lchan)
 		lchan->mgw_endpoint_ci_bts = NULL;
 	}
 
+	/* Ensure that the osmo_timer in lchan->active_cc is stopped. This is particularly important for lchan FSM
+	 * deallocation, so that the timer is no longer active when the lchan FSM instance gets discarded
+	 * (lchan_fsm_cleanup() calls this function), see OS#5554.
+	 *
+	 * Besides that, it is also good to make sure the timer is stopped when the lchan resets, to avoid any false
+	 * counts being accumulated, however obscure an error situation may be. */
+	osmo_time_cc_cleanup(&lchan->active_cc);
+
 	/* NUL all volatile state */
 	*lchan = (struct gsm_lchan){
 		.ts = lchan->ts,