intel: Add support for IPv6 IP-in-IP offload

This patch adds support for offloading IPXIP6 type packets that represent
either IPv4 or IPv6 encapsulated inside of an IPv6 outer IP header.  In
addition with this change we should also be able to support FOU
encapsulated traffic with outer IPv6 headers.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>