wireless : use a dedicated workqueue for cfg80211.

This patch moves the works cleanup, scan and events to a cfg80211
dedicated workqueue.

Platform driver like eeepc-laptop ought to use works to rfkill (as
new rfkill does lock in rfkill_unregister and the platform driver is
called from rfkill_switch_all which also lock the same mutex).
This raise a new issue in itself that the work scheduled by the platform
driver to the global worqueue calls wiphy_unregister which flush_work
scan and event works (which thus flush works on the global workqueue inside
a work on the global workqueue) and also put on hold the  wdev_cleanup_work
 (which prevents the dev_put on netdev thus indefinite Usage count error on
wifi device).

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Alban Browaeys <prahal@yahoo.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/wireless/core.h b/net/wireless/core.h
index a9db9e6..4ef3efc 100644
--- a/net/wireless/core.h
+++ b/net/wireless/core.h
@@ -91,6 +91,8 @@
 	return (wiphy_idx >= 0);
 }
 
+
+extern struct workqueue_struct *cfg80211_wq;
 extern struct mutex cfg80211_mutex;
 extern struct list_head cfg80211_rdev_list;
 extern int cfg80211_rdev_list_generation;