hyperv: Fix the total_data_buflen in send path

commit 942396b0 upstream.

total_data_buflen is used by netvsc_send() to decide if a packet can be put
into send buffer. It should also include the size of RNDIS message before the
Ethernet frame. Otherwise, a messge with total size bigger than send_section_size
may be copied into the send buffer, and cause data corruption.

[Request to include this patch to the Stable branches]
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/net/hyperv/netvsc_drv.c

@@ -556,6 +556,7 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 do_send:
 	/* Start filling in the page buffers with the rndis hdr */
 	rndis_msg->msg_len += rndis_msg_size;
+	packet->total_data_buflen = rndis_msg->msg_len;
 	packet->page_buf_cnt = init_page_array(rndis_msg, rndis_msg_size,
 					skb, &packet->page_buf[0]);