igc: Fix NFC rules with multicast addresses

Multicast MAC addresses are valid address for NFC rules but
igc_add_mac_filter() is currently rejecting them. In fact, the I225
controller doesn't impose any constraint on the address value so this
patch gets rid of the address validation check in MAC filter APIs.

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>