cfg80211: check iface combinations only when iface is running

commit f8cdddb8 upstream.

Don't validate interface combinations on a stopped
interface. Otherwise we might end up being able to
create a new interface with a certain type, but
won't be able to change an existing interface
into that type.

This also skips some other functions when
interface is stopped and changing interface type.
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/wireless/util.c

@@ -813,7 +813,7 @@ int cfg80211_change_iface(struct cfg80211_registered_device *rdev,
 	     ntype == NL80211_IFTYPE_P2P_CLIENT))
 		return -EBUSY;
 
-	if (ntype != otype) {
+	if (ntype != otype && netif_running(dev)) {
 		err = cfg80211_can_change_interface(rdev, dev->ieee80211_ptr,
 						    ntype);
 		if (err)