Merge changes from topic "test-tethering-icmp"

* changes:
  EthernetTetheringTest: add testTetherTcpV6
  EthernetTetheringTest: add testTetherTcpV4
  EthernetTetheringTest: add testIcmpv4Echo
  EthernetTetheringTest: add testTetherClatIcmp