qeth: avoid crash in case of layer mismatch for VSWITCH

For z/VM GuestLAN or VSWITCH devices the transport layer is
configured in z/VM. The layer2 attribute of a participating Linux
device has to match the z/VM definition. In case of a mismatch
Linux currently crashes in qeth recovery due to a reference to the
not yet existing net_device.
Solution: add a check for existence of net_device and add a message
pointing to the mismatch of layer definitions in Linux and z/VM.

Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/s390/net/qeth_l3_main.c b/drivers/s390/net/qeth_l3_main.c
index cdd6ab9..8f30085 100644
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -2082,9 +2082,11 @@
 		if (recovery_mode)
 			qeth_l3_stop(card->dev);
 		else {
-			rtnl_lock();
-			dev_close(card->dev);
-			rtnl_unlock();
+			if (card->dev) {
+				rtnl_lock();
+				dev_close(card->dev);
+				rtnl_unlock();
+			}
 		}
 		if (!card->use_hard_stop) {
 			rc = qeth_send_stoplan(card);