regulatory: use RCU to protect last_request

This will allow making freq_reg_info() lock-free.
Acked-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/regulatory.h

@@ -36,6 +36,7 @@ enum environment_cap {
 /**
  * struct regulatory_request - used to keep track of regulatory requests
  *
+ * @rcu_head: RCU head struct used to free the request
  * @wiphy_idx: this is set if this request's initiator is
  * 	%REGDOM_SET_BY_COUNTRY_IE or %REGDOM_SET_BY_DRIVER. This
  * 	can be used by the wireless core to deal with conflicts
@@ -73,6 +74,7 @@ enum environment_cap {
  * @list: used to insert into the reg_requests_list linked list
  */
 struct regulatory_request {
+	struct rcu_head rcu_head;
 	int wiphy_idx;
 	enum nl80211_reg_initiator initiator;
 	enum nl80211_user_reg_hint_type user_reg_hint_type;