mac80211: fix IBSS code to not sleep while atomic

With the RCU locking here we sleep while in an atomic context,
since we can sleep just use mutex locking for the interface
list instead of RCU. Sorry, seems I didn't get that in my UML
test.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/ibss.c b/net/mac80211/ibss.c
index 4f7a545..6030e00 100644
--- a/net/mac80211/ibss.c
+++ b/net/mac80211/ibss.c
@@ -784,14 +784,14 @@
 {
 	struct ieee80211_sub_if_data *sdata;
 
-	rcu_read_lock();
-	list_for_each_entry_rcu(sdata, &local->interfaces, list) {
+	mutex_lock(&local->iflist_mtx);
+	list_for_each_entry(sdata, &local->interfaces, list) {
 		if (sdata->vif.type != NL80211_IFTYPE_ADHOC)
 			continue;
 		sdata->u.ibss.last_scan_completed = jiffies;
 		ieee80211_sta_find_ibss(sdata);
 	}
-	rcu_read_unlock();
+	mutex_unlock(&local->iflist_mtx);
 }
 
 ieee80211_rx_result