[MAC80211]: fix add_interface monitor mode behaviour

This makes it behave the same whether we have monitor during operation
or not.
Signed-off-by: NJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: NJiri Benc <jbenc@suse.cz>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/mac80211/ieee80211.c

@@ -425,7 +425,10 @@ static int ieee80211_open(struct net_device *dev)
 
 	conf.if_id = dev->ifindex;
 	conf.type = sdata->type;
-	conf.mac_addr = dev->dev_addr;
+	if (sdata->type == IEEE80211_IF_TYPE_MNTR)
+		conf.mac_addr = NULL;
+	else
+		conf.mac_addr = dev->dev_addr;
 	res = local->ops->add_interface(local_to_hw(local), &conf);
 	if (res) {
 		if (sdata->type == IEEE80211_IF_TYPE_MNTR)