net: xen-netback: fix return type of ndo_start_xmit function

The method ndo_start_xmit() is defined as returning an 'netdev_tx_t',
which is a typedef for an enum type, so make sure the implementation in
this driver has returns 'netdev_tx_t' value, and change the function
return type to netdev_tx_t.

Found by coccinelle.
Signed-off-by: NYueHaibing <yuehaibing@huawei.com>
Acked-by: NWei Liu <wei.liu2@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/xen-netback/interface.c

@@ -165,7 +165,8 @@ static u16 xenvif_select_queue(struct net_device *dev, struct sk_buff *skb,
 	return vif->hash.mapping[skb_get_hash_raw(skb) % size];
 }
 
-static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
+static netdev_tx_t
+xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct xenvif *vif = netdev_priv(dev);
 	struct xenvif_queue *queue = NULL;