igc: Remove unused field from igc_nfc_filter

The 'cookie' field is not used anywhere in the code so this patch
removes it from struct igc_nfc_filter.

Signed-off-by: Andre Guedes <andre.guedes@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>