wireless: report reasonable bitrate for MCS rates through wext

Previously, cfg80211 had reported "0" for MCS (i.e. 802.11n) bitrates
through the wireless extensions interface.  However, nl80211 was
converting MCS rates into a reasonable bitrate number.  This patch moves
the nl80211 code to cfg80211 where it is now shared between both the
nl80211 interface and the wireless extensions interface.

Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/wireless/wext-compat.c b/net/wireless/wext-compat.c
index 584eb48..2fa8de11 100644
--- a/net/wireless/wext-compat.c
+++ b/net/wireless/wext-compat.c
@@ -1256,10 +1256,7 @@
 	if (!(sinfo.filled & STATION_INFO_TX_BITRATE))
 		return -EOPNOTSUPP;
 
-	rate->value = 0;
-
-	if (!(sinfo.txrate.flags & RATE_INFO_FLAGS_MCS))
-		rate->value = 100000 * sinfo.txrate.legacy;
+	rate->value = 100000 * cfg80211_calculate_bitrate(&sinfo.txrate);
 
 	return 0;
 }