sunvnet: add VIO v1.7 and v1.8 support

This patch adds support for VIO v1.7 (extended descriptor format)
and v1.8 (receive-side checksumming) to the sunvnet driver.

Signed-off-by: David L Stevens <david.stevens@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>