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/iface.c b/net/mac80211/iface.c
index 6b0d70e..c33feed 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -1181,6 +1181,13 @@
 		sband = local->hw.wiphy->bands[i];
 		sdata->rc_rateidx_mask[i] =
 			sband ? (1 << sband->n_bitrates) - 1 : 0;
+		if (sband)
+			memcpy(sdata->rc_rateidx_mcs_mask[i],
+			       sband->ht_cap.mcs.rx_mask,
+			       sizeof(sdata->rc_rateidx_mcs_mask[i]));
+		else
+			memset(sdata->rc_rateidx_mcs_mask[i], 0,
+			       sizeof(sdata->rc_rateidx_mcs_mask[i]));
 	}
 
 	/* setup type-dependent data */