Send empty LinkProperties when entering StoppedState.

Test: as follows
    - built
    - flashed
    - booted
    - runtest frameworks-net passes
    - changing from DHCPv4 to static while continuously pinging the
      default gateway works jsut fine
    - dumpsys log shows that during the change we send the empty LP:
  12-06 08:46:51.085 - CMD_ON_QUIT wlan0/23 0 0 null [rcvd_in=StoppingState, proc_in=StoppingState]
  12-06 08:46:51.092 - INVOKE onLinkPropertiesChange({{InterfaceName: wlan0 LinkAddresses: []  Routes: [] DnsAddresses: [] Domains: null MTU: 0}})

Bug: 69800563
Change-Id: I01047e9a72fce718a167c592bf14406c3bab3ba9