mac80211: fix race between connection monitor & suspend

When the connection monitor timer fires right before
suspend, the following will happen:
 timer fires -> monitor_work gets queued
 suspend calls ieee80211_sta_quiesce
 ieee80211_sta_quiesce:
  - deletes timer
  - cancels monitor_work synchronously, running it
  [note wrong order of these steps]
 monitor_work runs, re-arming the timer
 later, timer fires while system should be quiesced

This causes a warning:

WARNING: at net/mac80211/util.c:540 ieee80211_can_queue_work+0x35/0x40 [mac80211]()

but is otherwise harmless. I'm not completely sure
this is the scenario Thomas stumbled across, but it
is the only way I can right now see the warning in
a scenario like the one he reported.
Reported-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/mlme.c

@@ -2286,6 +2286,7 @@ void ieee80211_sta_quiesce(struct ieee80211_sub_if_data *sdata)
 
 	cancel_work_sync(&ifmgd->request_smps_work);
 
+	cancel_work_sync(&ifmgd->monitor_work);
 	cancel_work_sync(&ifmgd->beacon_connection_loss_work);
 	if (del_timer_sync(&ifmgd->timer))
 		set_bit(TMR_RUNNING_TIMER, &ifmgd->timers_running);
@@ -2294,7 +2295,6 @@ void ieee80211_sta_quiesce(struct ieee80211_sub_if_data *sdata)
 	if (del_timer_sync(&ifmgd->chswitch_timer))
 		set_bit(TMR_RUNNING_CHANSW, &ifmgd->timers_running);
 
-	cancel_work_sync(&ifmgd->monitor_work);
 	/* these will just be re-established on connection */
 	del_timer_sync(&ifmgd->conn_mon_timer);
 	del_timer_sync(&ifmgd->bcn_mon_timer);