cfg80211: don't require RTNL held for regdomain reads

The whole code is set up to allow RCU reads of this data, but
then uses rtnl_dereference() which requires the RTNL. Convert
it to rcu_dereference_rtnl() which makes it require only RCU
or the RTNL, to allow RCU-protected reading of the data.
Reviewed-by: Coelho, Luciano <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/reg.c

@@ -135,12 +135,12 @@ static void restore_regulatory_settings(bool reset_user);
 
 static const struct ieee80211_regdomain *get_cfg80211_regdom(void)
 {
-	return rtnl_dereference(cfg80211_regdomain);
+	return rcu_dereference_rtnl(cfg80211_regdomain);
 }
 
 const struct ieee80211_regdomain *get_wiphy_regdom(struct wiphy *wiphy)
 {
-	return rtnl_dereference(wiphy->regd);
+	return rcu_dereference_rtnl(wiphy->regd);
 }
 
 static const char *reg_dfs_region_str(enum nl80211_dfs_regions dfs_region)