xen-netback: add support for IPv6 checksum offload to guest

Check xenstore flag feature-ipv6-csum-offload to determine if a
guest is happy to accept IPv6 packets with only partial checksum.

Signed-off-by: Paul Durrant <[email protected]>
Cc: Wei Liu <[email protected]>
Cc: David Vrabel <[email protected]>
Cc: Ian Campbell <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
4 files changed