lchan_fsm: silently ignore LCHAN_EV_RLL_ERR_IND

The RLL ERR IND is sent by the BTS in any number of casese that lead
to a disconnect of a radio link layer, for example due to bad RF
conditions.  The lchan FSM currnently prints error messages about
this event not being permitted, leading to confusion among users.

Let's ignore this event, I don't think the lchan FSM should or could
be doing anything as a result.  We could also simply remove that event,
but let's keep it in case we should need it in the future.

Change-Id: I07aad62d25566d6068a95797915bb97fc3c66328

src/osmo-bsc/lchan_fsm.c

@@ -1336,6 +1336,13 @@ void lchan_fsm_allstate_action(struct osmo_fsm_inst *fi, uint32_t event, void *d
 		lchan_fail_to(LCHAN_ST_UNUSED, "LCHAN_EV_TS_ERROR");
 		return;
 
+	case LCHAN_EV_RLL_ERR_IND:
+		/* let's just ignore this.  We are already logging the
+		 * fact that this message was received inside
+		 * abis_rsl.c.  There can be any number of reasons why the
+		 * radio link layer failed */
+		return;
+
 	default:
 		return;
 	}
@@ -1464,6 +1471,7 @@ static struct osmo_fsm lchan_fsm = {
 	.allstate_action = lchan_fsm_allstate_action,
 	.allstate_event_mask = 0
 		| S(LCHAN_EV_TS_ERROR)
+		| S(LCHAN_EV_RLL_ERR_IND)
 		,
 	.timer_cb = lchan_fsm_timer_cb,
 	.cleanup = lchan_fsm_cleanup,