mac80211: cancel restart_work explicitly instead of depending on flush_scheduled_work()

iee80211_hw->restart_work is the only work which uses the system
workqueue.  Instead of calling flush_scheduled_work() during
iee80211_exit(), cancel the work during unregistration.

This is to prepare for the deprecation and removal of
flush_scheduled_work().
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/mac80211/main.c

@@ -748,7 +748,7 @@ int ieee80211_register_hw(struct ieee80211_hw *hw)
 		hw->queues = IEEE80211_MAX_QUEUES;
 
 	local->workqueue =
-		create_singlethread_workqueue(wiphy_name(local->hw.wiphy));
+		alloc_ordered_workqueue(wiphy_name(local->hw.wiphy), 0);
 	if (!local->workqueue) {
 		result = -ENOMEM;
 		goto fail_workqueue;
@@ -962,12 +962,6 @@ static void __exit ieee80211_exit(void)
 	rc80211_minstrel_ht_exit();
 	rc80211_minstrel_exit();
 
-	/*
-	 * For key todo, it'll be empty by now but the work
-	 * might still be scheduled.
-	 */
-	flush_scheduled_work();
-
 	if (mesh_allocated)
 		ieee80211s_stop();