virtio_net: fix csum generation for virtio-net devices

The commit e858fae2b0b8 ("virtio_net: use common code for virtio_net_hdr
and skb GSO conversion") replaced the tun code for header manipulation
with the generic helpers. While doing so, it implictly moved the
skb_partial_csum_set() invocation after eth_type_trans(), which
invalidate the current gso start/offset values.
Fix it by moving the helper invocation before the mac pulling.

Fixes: e858fae2b0b8 ("virtio_net: use common code for virtio_net_hdr and
skb GSO conversion")

Reported-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -482,10 +482,6 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
 	if (hdr->hdr.flags & VIRTIO_NET_HDR_F_DATA_VALID)
 		skb->ip_summed = CHECKSUM_UNNECESSARY;
 
-	skb->protocol = eth_type_trans(skb, dev);
-	pr_debug("Receiving skb proto 0x%04x len %i type %i\n",
-		 ntohs(skb->protocol), skb->len, skb->pkt_type);
-
 	if (virtio_net_hdr_to_skb(skb, &hdr->hdr,
 				  virtio_is_little_endian(vi->vdev))) {
 		net_warn_ratelimited("%s: bad gso: type: %u, size: %u\n",
@@ -494,6 +490,10 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
 		goto frame_err;
 	}
 
+	skb->protocol = eth_type_trans(skb, dev);
+	pr_debug("Receiving skb proto 0x%04x len %i type %i\n",
+		 ntohs(skb->protocol), skb->len, skb->pkt_type);
+
 	napi_gro_receive(&rq->napi, skb);
 	return;