um: vector netdev: adjust to xmit_more API change

Replace skb->xmit_more usage by netdev_xmit_more().

Fixes: 4f296ede ("drivers: net: aurora: use netdev_xmit_more helper")
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/um/drivers/vector_kern.c

@@ -1043,7 +1043,7 @@ static int vector_net_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		vector_send(vp->tx_queue);
 		return NETDEV_TX_OK;
 	}
-	if (skb->xmit_more) {
+	if (netdev_xmit_more()) {
 		mod_timer(&vp->tl, vp->coalesce);
 		return NETDEV_TX_OK;
 	}