igc: Return -EOPNOTSUPP when VLAN mask doesn't match

The I225 controller supports Rx queue assignment based on VLAN priority
only. Other Tag Control Information (TCI) are valid, but not supported
by the driver. So this patch changes the returning code from igc_add_
ethtool_nfc_entry() to -EOPNOTSUPP in order to provide more meaningful
information on why the function failed.

It also adds a debug messages to give the user a hint about what went
wrong with the NFC setup.

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>