virtio-net: Support IFF_TX_SKB_NO_LINEAR flag

Virtio net supports the case where the skb linear space is empty, so
add priv_flags.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210218204908.5455-4-alobakin@pm.me

drivers/net/virtio_net.c

@@ -2972,7 +2972,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 		return -ENOMEM;
 
 	/* Set up network device as normal. */
-	dev->priv_flags |= IFF_UNICAST_FLT | IFF_LIVE_ADDR_CHANGE;
+	dev->priv_flags |= IFF_UNICAST_FLT | IFF_LIVE_ADDR_CHANGE |
+			   IFF_TX_SKB_NO_LINEAR;
 	dev->netdev_ops = &virtnet_netdev;
 	dev->features = NETIF_F_HIGHDMA;