mac80211: make noack test available

There's this internal wifi_wme_noack_test variable that
we use to set the QoS control if set. For one, it is
unlikely that it is set. Secondly, if set it needs to
influence the IEEE80211_TX_CTL_NO_ACK TX control flag,
and finally we should also be able to set it at all, so
make it available in debugfs.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 5f9a8d7..8f68bf9 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1087,7 +1087,10 @@
 		info->flags |= IEEE80211_TX_CTL_NO_ACK;
 	} else {
 		tx->flags |= IEEE80211_TX_UNICAST;
-		info->flags &= ~IEEE80211_TX_CTL_NO_ACK;
+		if (unlikely(local->wifi_wme_noack_test))
+			info->flags |= IEEE80211_TX_CTL_NO_ACK;
+		else
+			info->flags &= ~IEEE80211_TX_CTL_NO_ACK;
 	}
 
 	if (tx->flags & IEEE80211_TX_FRAGMENTED) {