i40e/i40evf: Handle IPv6 extension headers in checksum offload

i40e/i40evf: Handle IPv6 extension headers in checksum offload

Orabug: 22342532

This patch adds support for IPv6 extension headers in setting up the Tx
checksum.  Without this patch extension headers would cause IPv6 traffic to
fail as the transport protocol could not be identified.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit a3fd9d8876a589f05725237aced606b995956860)
Signed-off-by: Brian Maly <brian.maly@oracle.com>