mac80211: explain padding in place of rate field

Apparently this was confusing still ... add a
note that the byte is needed as padding.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/rx.c

@@ -143,7 +143,8 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
 	if (status->flag & RX_FLAG_HT) {
 		/*
 		 * MCS information is a separate field in radiotap,
-		 * added below.
+		 * added below. The byte here is needed as padding
+		 * for the channel though, so initialise it to 0.
 		 */
 		*pos = 0;
 	} else {