hv_netvsc: Fix book keeping of skb during batching process

Since eliminating send_completion_tid from struct hv_netvsc_packet, we
haven't add proper book keeping for the skb of the batched packet. This
patch fixes this issue and allows the previous skb is properly freed.
Otherwise, a panic may happen.
Thanks to Simon Xiao <sixiao@microsoft.com> for bisecting and analysis.

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>
diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index f4130af..fcb92c0 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h
@@ -624,6 +624,7 @@
 #define RNDIS_PKT_ALIGN_DEFAULT 8
 
 struct multi_send_data {
+	struct sk_buff *skb; /* skb containing the pkt */
 	struct hv_netvsc_packet *pkt; /* netvsc pkt pending */
 	u32 count; /* counter of batched packets */
 };