ixgbe: Add UDP segmentation offload support

Repost from a series by Alexander Duyck to add UDP segmentation offload
support to the igb driver:
https://lore.kernel.org/netdev/20180504003916.4769.66271.stgit@localhost.localdomain/



CC: Alexander Duyck <alexander.h.duyck@intel.com>
CC: Willem de Bruijn <willemb@google.com>
Suggested-by: Alexander Duyck <alexander.h.duyck@intel.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>