ieee80211: add IEEE80211_COUNTRY_STRING_LEN definition

and make use of it in wireless drivers

Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/libertas/host.h b/drivers/net/wireless/libertas/host.h
index 5eac135..6cb6935 100644
--- a/drivers/net/wireless/libertas/host.h
+++ b/drivers/net/wireless/libertas/host.h
@@ -387,7 +387,7 @@
 struct mrvl_ie_domain_param_set {
 	struct mrvl_ie_header header;
 
-	u8 country_code[3];
+	u8 country_code[IEEE80211_COUNTRY_STRING_LEN];
 	struct ieee80211_country_ie_triplet triplet[MAX_11D_TRIPLETS];
 } __packed;