mac80211: Fix sta_mtx unlocking on insert STA failure path

Commit 34e89507 introduced sta_mtx
locking into sta_info_insert() (now sta_info_insert_rcu), but forgot
to unlock this mutex on one of the error paths. Fix this by adding
the missing mutex_unlock() call for the case where STA insert fails
due to an entry existing already. This may happen at least in AP mode
when a STA roams between two BSSes (vifs).
Signed-off-by: NJouni Malinen <j@w1.fi>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/mac80211/sta_info.c

@@ -434,6 +434,7 @@ int sta_info_insert_rcu(struct sta_info *sta) __acquires(RCU)
 	/* check if STA exists already */
 	if (sta_info_get_bss(sdata, sta->sta.addr)) {
 		spin_unlock_irqrestore(&local->sta_lock, flags);
+		mutex_unlock(&local->sta_mtx);
 		rcu_read_lock();
 		err = -EEXIST;
 		goto out_free;