mac80211: constify ieee80211_if_conf.bssid

Then one place can be a static const.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 9a5869e..ef42559 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -643,7 +643,7 @@
  */
 struct ieee80211_if_conf {
 	u32 changed;
-	u8 *bssid;
+	const u8 *bssid;
 };
 
 /**