i40e: Fix bug with TCP over IPv6 over VXLAN

The driver was examining the outer protocol layer to set the inner protocol
layer checksum offload.  In the case of TCP over IPV6 over an IPv4 based
VXLAN the inner checksum offloads would be set to look for IPv4/UDP instead
of IPv6/TCP.  This code fixes that so that the driver will look at the
proper layer for encapsulation offload settings.

Signed-off-by: Anjali Singhai <anjali.singhai@intel.com>
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>