p54: fix tx feedback status flag check

Michael reported that p54* never really entered power
save mode, even tough it was enabled.

It turned out that upon a power save mode change the
firmware will set a special flag onto the last outgoing
frame tx status (which in this case is almost always the
designated PSM nullfunc frame). This flag confused the
driver; It erroneously reported transmission failures
to the stack, which then generated the next nullfunc.
and so on...

Cc: <stable@kernel.org>
Reported-by: NMichael Buesch <mb@bu3sch.de>
Tested-by: NMichael Buesch <mb@bu3sch.de>
Signed-off-by: NChristian Lamparter <chunkeey@googlemail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/p54/txrx.c

@@ -446,7 +446,7 @@ static void p54_rx_frame_sent(struct p54_common *priv, struct sk_buff *skb)
 	}
 
 	if (!(info->flags & IEEE80211_TX_CTL_NO_ACK) &&
-	     (!payload->status))
+	     !(payload->status & P54_TX_FAILED))
 		info->flags |= IEEE80211_TX_STAT_ACK;
 	if (payload->status & P54_TX_PSM_CANCELLED)
 		info->flags |= IEEE80211_TX_STAT_TX_FILTERED;