i40e: fix VLAN inside VXLAN

Previously to this patch, the hardware was removing
VLAN tags from the inner header of VXLAN packets.  The
hardware configuration can be changed to leave the
packet alone since that is what the linux stack
expects for this type of VLAN in VXLAN packet.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>