virtio-net: correctly xmit linearized page on XDP_TX

After we linearize page, we should xmit this page instead of the page
of first buffer which may lead unexpected result. With this patch, we
can see correct packet during XDP_TX.

Cc: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>
Acked-by: NJohn Fastabend <john.r.fastabend@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -572,7 +572,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
 			goto err_xdp;
 
-		act = do_xdp_prog(vi, rq, xdp_prog, page, offset, len);
+		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
 		switch (act) {
 		case XDP_PASS:
 			if (unlikely(xdp_page != page))