netvsc: negotiate checksum and segmentation parameters

netvsc: negotiate checksum and segmentation parameters

Redo how Hyper-V network driver negotiates offload features. Query the
host to determine offload settings, and use the result.

Also:
  * disable IPv4 header checksum offload (not used by Linux)
  * enable TSO only if host supports
  * enable UDP checksum offload if supported
  * don't advertise support for checksumming of non-IP protocols
  * adjust GSO maximum segment size
  * enable HIGHDMA

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>