regulatory: use RCU to protect global and wiphy regdomains

To simplify the locking and not require cfg80211_mutex
(which nl80211 uses to access the global regdomain) and
also to make it possible for drivers to access their
wiphy->regd safely, use RCU to protect these pointers.

Acked-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/regulatory.h

@@ -18,6 +18,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include <linux/rcupdate.h>
 
 /**
  * enum environment_cap - Environment parsed from country IE
@@ -101,6 +102,7 @@ struct ieee80211_reg_rule {
 };
 
 struct ieee80211_regdomain {
+	struct rcu_head rcu_head;
 	u32 n_reg_rules;
 	char alpha2[2];
 	u8 dfs_region;