veth: Fixing transmit return status for dropped packets

The veth_xmit function returns NETDEV_TX_OK even when packets are dropped.
This behavior leads to incorrect calculations of statistics counts, as
well as things like txq->trans_start updates.

Fixes: e314dbd ("[NET]: Virtual ethernet device driver.")
Signed-off-by: Liang Chen <liangchen.linux@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/veth.c

@@ -344,6 +344,7 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct veth_priv *rcv_priv, *priv = netdev_priv(dev);
 	struct veth_rq *rq = NULL;
+	int ret = NETDEV_TX_OK;
 	struct net_device *rcv;
 	int length = skb->len;
 	bool use_napi = false;
@@ -378,11 +379,12 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
 	} else {
 drop:
 		atomic64_inc(&priv->dropped);
+		ret = NET_XMIT_DROP;
 	}
 
 	rcu_read_unlock();
 
-	return NETDEV_TX_OK;
+	return ret;
 }
 
 static u64 veth_stats_tx(struct net_device *dev, u64 *packets, u64 *bytes)