cfg80211: allow only the core to request to update the world regdom

It seems some out of tree drivers were using a regulatory_hint("00")
to trigger off the wiphy regulatory notifier, for those cases just
setting the WIPHY_FLAG_CUSTOM_REGULATORY would suffice to call
the reg_notifier() for a world regulatory domain update. If drivers
find other needs for calling the reg_notifier() a proper implemenation
is preferred.
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/reg.c

@@ -2200,6 +2200,8 @@ static int __set_regdom(const struct ieee80211_regdomain *rd)
 		return -EINVAL;
 
 	if (is_world_regdom(rd->alpha2)) {
+		if (lr->initiator != NL80211_REGDOM_SET_BY_CORE)
+			return -EINVAL;
 		update_world_regdomain(rd);
 		return 0;
 	}