s390/qeth: fix L2 header access in qeth_l3_osa_features_check()

ip_finish_output_gso() may call .ndo_features_check() even before the
skb has a L2 header. This conflicts with qeth_get_ip_version()'s attempt
to inspect the L2 header via vlan_eth_hdr().

Switch to vlan_get_protocol(), as already used further down in the
common qeth_features_check() path.

Fixes: f13ade19 ("s390/qeth: run non-offload L3 traffic over common xmit path")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/s390/net/qeth_l3_main.c

@@ -1813,7 +1813,7 @@ static netdev_features_t qeth_l3_osa_features_check(struct sk_buff *skb,
 						    struct net_device *dev,
 						    netdev_features_t features)
 {
-	if (qeth_get_ip_version(skb) != 4)
+	if (vlan_get_protocol(skb) != htons(ETH_P_IP))
 		features &= ~NETIF_F_HW_VLAN_CTAG_TX;
 	return qeth_features_check(skb, dev, features);
 }