mac80211: fix offchannel TX cookie matching

When I introduced in-kernel off-channel TX I
introduced a bug -- the work can't be canceled
again because the code clear the skb pointer.
Fix this by keeping track separately of whether
TX status has already been reported.

Cc: stable@kernel.org [2.6.38+]
Reported-by: Jouni Malinen <j@w1.fi>
Tested-by: Jouni Malinen <j@w1.fi>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/status.c b/net/mac80211/status.c
index 864a9c3..f3d7107 100644
--- a/net/mac80211/status.c
+++ b/net/mac80211/status.c
@@ -429,7 +429,7 @@
 				continue;
 			if (wk->offchan_tx.frame != skb)
 				continue;
-			wk->offchan_tx.frame = NULL;
+			wk->offchan_tx.status = true;
 			break;
 		}
 		rcu_read_unlock();