sunvnet: fix NULL pointer dereference

This patch fixes a NULL pointer dereference when __tx_port_find() doesn't
find a matching port.
Signed-off-by: David L Stevens <david.stevens@oracle.com>
Acked-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sun/sunvnet.c

@@ -958,6 +958,8 @@ vnet_select_queue(struct net_device *dev, struct sk_buff *skb,
 	struct vnet *vp = netdev_priv(dev);
 	struct vnet_port *port = __tx_port_find(vp, skb);
 
+	if (port == NULL)
+		return 0;
 	return port->q_index;
 }