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/include/net/mac80211.h b/include/net/mac80211.h
index df1004b..0c2676e 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -4555,8 +4555,8 @@
 			   struct ieee80211_sta *pubsta,
 			   struct ieee80211_sta_rates *rates);
 
-int ieee80211_rate_control_register(struct rate_control_ops *ops);
-void ieee80211_rate_control_unregister(struct rate_control_ops *ops);
+int ieee80211_rate_control_register(const struct rate_control_ops *ops);
+void ieee80211_rate_control_unregister(const struct rate_control_ops *ops);
 
 static inline bool
 conf_is_ht20(struct ieee80211_conf *conf)