qeth: fix race condition during device startup

QDIO is running independent from netdevice state. We are not
allowed to schedule NAPI in case the netdevice is not open.
Signed-off-by: NFrank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/s390/net/qeth_core_main.c

@@ -2903,7 +2903,7 @@ void qeth_qdio_start_poll(struct ccw_device *ccwdev, int queue,
 {
 	struct qeth_card *card = (struct qeth_card *)card_ptr;
 
-	if (card->dev)
+	if (card->dev && (card->dev->flags & IFF_UP))
 		napi_schedule(&card->napi);
 }
 EXPORT_SYMBOL_GPL(qeth_qdio_start_poll);