hv_netvsc: Add structs and handlers for VF messages

This patch adds data structures and handlers for messages related
to SRIOV Virtual Function.

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>