Add test coverage for cleanup bug to be fixed.

The test calls that need to pass but do not currently are commented out.

Test: as follows
    - built (bullhead)
    - flashed
    - booted
    - runtest -x .../tethering/TetherInterfaceStateMachineTest.java passes
Bug: 32031803
Bug: 32163131

Change-Id: I68ed476920bef882f353d8e8a54c72120bc27002