Based on a series from Alexander Duyck this change adds UDP segmentation
offload support to the igb 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: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>