iwlegacy: add flush callback

Dump implementation of flush, which just wait until all TX queues
become empty.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlegacy/3945-mac.c b/drivers/net/wireless/iwlegacy/3945-mac.c
index d604b40..962400a 100644
--- a/drivers/net/wireless/iwlegacy/3945-mac.c
+++ b/drivers/net/wireless/iwlegacy/3945-mac.c
@@ -3474,6 +3474,7 @@
 	.sta_add = il3945_mac_sta_add,
 	.sta_remove = il_mac_sta_remove,
 	.tx_last_beacon = il_mac_tx_last_beacon,
+	.flush = il_mac_flush,
 };
 
 static int