mac80211: count interfaces correctly for combination checks

Since moving the interface combination checks to mac80211, it's
broken because it now only considers interfaces with an assigned
channel context, so for example any interface that isn't active
can still be up, which is clearly an issue; also, in particular
P2P-Device wdevs are an issue since they never have a chanctx.

Fix this by counting running interfaces instead the ones with a
channel context assigned.

Cc: [email protected] [3.16+]
Fixes: 73de86a ("cfg80211/mac80211: move interface counting for combination check to mac80211")
Signed-off-by: Andrei Otcheretianski <[email protected]>
Signed-off-by: Emmanuel Grumbach <[email protected]>
[rewrite commit message, dig out the commit it fixes]
Signed-off-by: Johannes Berg <[email protected]>

net/mac80211/util.c

@@ -3178,7 +3178,7 @@ int ieee80211_check_combinations(struct ieee80211_sub_if_data *sdata,
 		wdev_iter = &sdata_iter->wdev;
 
 		if (sdata_iter == sdata ||
-		    rcu_access_pointer(sdata_iter->vif.chanctx_conf) == NULL ||
+		    !ieee80211_sdata_running(sdata_iter) ||
 		    local->hw.wiphy->software_iftypes & BIT(wdev_iter->iftype))
 			continue;