hv_netvsc: Eliminate send_completion from struct hv_netvsc_packet

Eliminate send_completion from struct hv_netvsc_packet.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>