mac80211: Warn if the rate controller requests retries for a NO_ACK frame

To deter future rate scaling algorithm writers from requesting NO_ACK
packets to be retried, throw a WARN_ON_ONCE if the algorithm hands us
a try count over 1 for NO_ACK packet.
Signed-off-by: NGábor Stefanik <netrolller.3d@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/mac80211/tx.c

@@ -558,6 +558,10 @@ ieee80211_tx_h_rate_ctrl(struct ieee80211_tx_data *tx)
 	if (unlikely(!info->control.rates[0].count))
 		info->control.rates[0].count = 1;
 
+	if (WARN_ON_ONCE((info->control.rates[0].count > 1) &&
+			 (info->flags & IEEE80211_TX_CTL_NO_ACK)))
+		info->control.rates[0].count = 1;
+
 	if (is_multicast_ether_addr(hdr->addr1)) {
 		/*
 		 * XXX: verify the rate is in the basic rateset