MAC addresses from all interfaces.

def GetMacAddresses(self):
    """MAC addresses from all interfaces."""
    result = set()
    for interface in self.interfaces:
      if (interface.mac_address and
          interface.mac_address != b"\x00" * len(interface.mac_address)):
        result.add(Text(interface.mac_address.human_readable_address))
    return sorted(result)