cfg80211: sched_scan_mtx lock in cfg80211_conn_work()

Introduced in f9f4752
("cfg80211: always check for scan end on P2P device")

cfg80211_conn_scan() which requires sched_scan_mtx to be held can be called
from cfg80211_conn_work(). Without this we are hitting multiple warnings like
the following:

WARNING: at net/wireless/sme.c:88 cfg80211_conn_scan+0x1dc/0x3a0 [cfg80211]()
Hardware name: 0578A21
Modules linked in: ...
Pid: 620, comm: kworker/3:1 Not tainted 3.9.0-rc4-next-20130328+ #326
Call Trace:
 [<c1036992>] warn_slowpath_common+0x72/0xa0
 [<c10369e2>] warn_slowpath_null+0x22/0x30
 [<faa4b0ec>] cfg80211_conn_scan+0x1dc/0x3a0 [cfg80211]
 [<faa4b344>] cfg80211_conn_do_work+0x94/0x380 [cfg80211]
 [<faa4c3b2>] cfg80211_conn_work+0xa2/0x130 [cfg80211]
 [<c1051858>] process_one_work+0x198/0x450

Signed-off-by: Artem Savkov <artem.savkov@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/sme.c

@@ -224,6 +224,7 @@ void cfg80211_conn_work(struct work_struct *work)
 	rtnl_lock();
 	cfg80211_lock_rdev(rdev);
 	mutex_lock(&rdev->devlist_mtx);
+	mutex_lock(&rdev->sched_scan_mtx);
 
 	list_for_each_entry(wdev, &rdev->wdev_list, list) {
 		wdev_lock(wdev);
@@ -248,6 +249,7 @@ void cfg80211_conn_work(struct work_struct *work)
 		wdev_unlock(wdev);
 	}
 
+	mutex_unlock(&rdev->sched_scan_mtx);
 	mutex_unlock(&rdev->devlist_mtx);
 	cfg80211_unlock_rdev(rdev);
 	rtnl_unlock();