Merge changes I44e85c09,I01810b54,I1c169311,I15f2aeac,I048512a1 into main

* changes:
  Use AutoCloseTestInterfaceRule in NsdManagerDownstreamTetheringTest
  Add auto close rule for test interfaces
  Add finalizer to check whether destroy was called
  Wrap use of test interface in EthernetTestInterface
  Add a class to properly manage ethernet test interfaces