net/packet: fix packet drop as of virtio gso

When we use raw socket as the vhost backend, a packet from virito with
gso offloading information, cannot be sent out in later validaton at
xmit path, as we did not set correct skb->protocol which is further used
for looking up the gso function.

To fix this, we set this field according to virito hdr information.

Fixes: e858fae2b0b8f4 ("virtio_net: use common code for virtio_net_hdr and skb GSO conversion")
Signed-off-by: Jianfeng Tan <jianfeng.tan@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 9397628..cb462f9 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -5,6 +5,24 @@
 #include <linux/if_vlan.h>
 #include <uapi/linux/virtio_net.h>
 
+static inline int virtio_net_hdr_set_proto(struct sk_buff *skb,
+					   const struct virtio_net_hdr *hdr)
+{
+	switch (hdr->gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
+	case VIRTIO_NET_HDR_GSO_TCPV4:
+	case VIRTIO_NET_HDR_GSO_UDP:
+		skb->protocol = cpu_to_be16(ETH_P_IP);
+		break;
+	case VIRTIO_NET_HDR_GSO_TCPV6:
+		skb->protocol = cpu_to_be16(ETH_P_IPV6);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
 					const struct virtio_net_hdr *hdr,
 					bool little_endian)