regulatory: add NUL to request alpha2

Similar to the ancient commit a5fe8e7 ("regulatory: add NUL
to alpha2"), add another byte to alpha2 in the request struct so
that when we use nla_put_string(), we don't overrun anything.

Fixes: 73d54c9 ("cfg80211: add regulatory netlink multicast group")
Reported-by: Kees Cook <keescook@google.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/regulatory.h

@@ -78,7 +78,7 @@ struct regulatory_request {
 	int wiphy_idx;
 	enum nl80211_reg_initiator initiator;
 	enum nl80211_user_reg_hint_type user_reg_hint_type;
-	char alpha2[2];
+	char alpha2[3];
 	enum nl80211_dfs_regions dfs_region;
 	bool intersect;
 	bool processed;