mac80211: add support for mcs masks

* Handle MCS masks set by the user.
* Match rates provided by the rate control algorithm to the mask set,
  also in HT mode, and switch back to legacy mode if necessary.
* add debugfs files to observate the rate selection

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
index ca6486b..d47e8c1 100644
--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -646,6 +646,7 @@
 
 	/* bitmap of allowed (non-MCS) rate indexes for rate control */
 	u32 rc_rateidx_mask[IEEE80211_NUM_BANDS];
+	u8  rc_rateidx_mcs_mask[IEEE80211_NUM_BANDS][IEEE80211_HT_MCS_MASK_LEN];
 
 	union {
 		struct ieee80211_if_ap ap;