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>

net/mac80211/ieee80211_i.h

@@ -346,6 +346,7 @@ struct ieee80211_work {
 		struct {
 			struct sk_buff *frame;
 			u32 wait;
+			bool status;
 		} offchan_tx;
 	};