be2net: changes for checksum and segmentation offload

- Enables Rx checksum feature by default.
- Disables support for ipv6 tso.
- Changes in Rx path to handle Rx completions with various checksum options.

Signed-off-by: Ajit Khaparde <ajitk@serverengines.com>
Signed-off-by: David S. Miller <davem@davemloft.net>