mac80211: push interface checks down

This patch pushes the "netif_running()" and "same type as before"
checks down into ieee80211_if_change_type() to centralise the
logic instead of duplicating it for cfg80211 and wext.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index 35bcdfe..2146c0c 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -930,8 +930,8 @@
 int ieee80211_if_add(struct ieee80211_local *local, const char *name,
 		     struct net_device **new_dev, enum ieee80211_if_types type,
 		     struct vif_params *params);
-void ieee80211_if_change_type(struct ieee80211_sub_if_data *sdata,
-			      enum ieee80211_if_types type);
+int ieee80211_if_change_type(struct ieee80211_sub_if_data *sdata,
+			     enum ieee80211_if_types type);
 void ieee80211_if_remove(struct net_device *dev);
 void ieee80211_remove_interfaces(struct ieee80211_local *local);