mac80211: make rate control ops const

Change the code to allow making all the rate control ops
const, nothing ever needs to change them. Also change all
drivers to make use of this and mark the ops const.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/net/mac80211/rate.h b/net/mac80211/rate.h
index b95e16c..9aa2a11 100644
--- a/net/mac80211/rate.h
+++ b/net/mac80211/rate.h
@@ -21,7 +21,7 @@
 
 struct rate_control_ref {
 	struct ieee80211_local *local;
-	struct rate_control_ops *ops;
+	const struct rate_control_ops *ops;
 	void *priv;
 };