hv_netvsc: add software transmit timestamp support

BugLink: http://bugs.launchpad.net/bugs/1583357

Enable skb_tx_timestamp in hyperv netvsc.
Signed-off-by: Simon Xiao <sixiao@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 76d13b56)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/net/hyperv/netvsc_drv.c

@@ -550,6 +550,8 @@ static int netvsc_start_xmit(struct sk_buff *skb, struct net_device *net)
 	packet->page_buf_cnt = init_page_array(rndis_msg, rndis_msg_size,
 					       skb, packet, &pb);
 
+	/* timestamp packet in software */
+	skb_tx_timestamp(skb);
 	ret = netvsc_send(net_device_ctx->device_ctx, packet,
 			  rndis_msg, &pb, skb);
 
@@ -920,6 +922,7 @@ static const struct ethtool_ops ethtool_ops = {
 	.get_link	= ethtool_op_get_link,
 	.get_channels   = netvsc_get_channels,
 	.set_channels   = netvsc_set_channels,
+	.get_ts_info	= ethtool_op_get_ts_info,
 };
 
 static const struct net_device_ops device_ops = {