igc: Enable NFC rules based source MAC address

This patch adds support for Network Flow Classification (NFC) rules
based on source MAC address. Note that the controller doesn't support
rules with both source and destination addresses set, so this special
case is checked in igc_add_ethtool_nfc_entry().

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>