loopback interface: added loopback interface implementation
loopback interface: using loopback interface
loopback interface: fingerprints changed - these tests/examples uses lo0 interface
loopback interface: fixed module tests

- networkLayerGateIndex incremented (lo0 is index=0)
- link local addresses (generated by FlatNetworkConfigurator6) changed,
  because the address calculation based on networkLayerGateIndex.
- added lo0 interface for dhcp_2 test
loopback interface: added module tests