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/drivers/net/wireless/rtlwifi/rc.c b/drivers/net/wireless/rtlwifi/rc.c
index a98acef..1503d9e 100644
--- a/drivers/net/wireless/rtlwifi/rc.c
+++ b/drivers/net/wireless/rtlwifi/rc.c
@@ -260,7 +260,7 @@
 	kfree(rate_priv);
 }
 
-static struct rate_control_ops rtl_rate_ops = {
+static const struct rate_control_ops rtl_rate_ops = {
 	.module = NULL,
 	.name = "rtl_rc",
 	.alloc = rtl_rate_alloc,