qeth: repair crash in qeth_l3_vlan_rx_kill_vid()

Commit efc73f4b "net: Fix memory leak - vlan_info struct" adds deletion of
VLAN 0 for devices with feature NETIF_F_HW_VLAN_FILTER. For driver
qeth these are the layer 3 devices. Usually there exists no
separate vlan net_device for VLAN 0. Thus the qeth functions
qeth_l3_free_vlan_addresses4() and qeth_l3_free_vlan_addresses6()
require an extra checking if function __vlan_find_dev_deep()
returns with a net_device.

Cc: stable@vger.kernel.org
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>

drivers/s390/net/qeth_l3_main.c

@@ -1758,6 +1758,8 @@ static void qeth_l3_free_vlan_addresses4(struct qeth_card *card,
 	QETH_CARD_TEXT(card, 4, "frvaddr4");
 
 	netdev = __vlan_find_dev_deep(card->dev, vid);
+	if (!netdev)
+		return;
 	in_dev = in_dev_get(netdev);
 	if (!in_dev)
 		return;
@@ -1786,6 +1788,8 @@ static void qeth_l3_free_vlan_addresses6(struct qeth_card *card,
 	QETH_CARD_TEXT(card, 4, "frvaddr6");
 
 	netdev = __vlan_find_dev_deep(card->dev, vid);
+	if (!netdev)
+		return;
 	in6_dev = in6_dev_get(netdev);
 	if (!in6_dev)
 		return;