mac80211: revamp beacon configuration

This patch changes mac80211's beacon configuration handling
to never pass skbs to the driver directly but rather always
require the driver to use ieee80211_beacon_get(). Additionally,
it introduces "change flags" on the config_interface() call
to enable drivers to figure out what is changing. Finally, it
removes the beacon_update() driver callback in favour of
having IBSS beacon delivered by ieee80211_beacon_get() as well.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/wext.c b/net/mac80211/wext.c
index c041db9..34fa8ed 100644
--- a/net/mac80211/wext.c
+++ b/net/mac80211/wext.c
@@ -444,7 +444,7 @@
 		memset(sdata->u.ap.ssid + len, 0,
 		       IEEE80211_MAX_SSID_LEN - len);
 		sdata->u.ap.ssid_len = len;
-		return ieee80211_if_config(dev);
+		return ieee80211_if_config(sdata, IEEE80211_IFCC_SSID);
 	}
 	return -EOPNOTSUPP;
 }