igb: Add the skeletons for tc-flower offloading

This adds basic functions needed to implement offloading for filters
created by tc-flower.

Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>