cfg80211/mac80211: move more combination checks to mac80211

Get rid of the cfg80211_can_add_interface() and
cfg80211_can_change_interface() functions by moving that functionality
to mac80211.  With this patch all interface combination checks are now
out of cfg80211 (except for the channel switch case which will be
addressed in a future commit).

Additionally, modify the ieee80211_check_combinations() function so
that an undefined chandef can be passed, in order to use it before a
channel is defined.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 2b99aad33..232d15c 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -8969,9 +8969,8 @@
 	if (wdev->p2p_started)
 		return 0;
 
-	err = cfg80211_can_add_interface(rdev, wdev->iftype);
-	if (err)
-		return err;
+	if (rfkill_blocked(rdev->rfkill))
+		return -ERFKILL;
 
 	err = rdev_start_p2p_device(rdev, wdev);
 	if (err)