qeth: tagging with VLAN-ID 0

This patch adapts qeth to handle tagged frames with VLAN-ID 0 and
with or without priority information in the tag. It enables qeth to
receive priority-tagged frames on a base interface, for example from
z/OS, without configuring an additional VLAN interface.

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_l2_main.c b/drivers/s390/net/qeth_l2_main.c
index 01c3c1f..847e8797 100644
--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -310,6 +310,8 @@
 	struct qeth_vlan_vid *id;
 
 	QETH_CARD_TEXT_(card, 4, "aid:%d", vid);
+	if (!vid)
+		return;
 	if (card->info.type == QETH_CARD_TYPE_OSM) {
 		QETH_CARD_TEXT(card, 3, "aidOSM");
 		return;