i40e: Add UDP segmentation offload support

Based on a series from Alexander Duyck this change adds UDP segmentation
offload support to the i40e driver.

CC: Alexander Duyck <alexander.h.duyck@intel.com>
CC: Willem de Bruijn <willemb@google.com>
Signed-off-by: Josh Hunt <johunt@akamai.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>