Minor improvement in logging in TetheringConfiguration

Test: as follows
    - built
    - booted
    - flashed
    - runtest frameworks-net passes
    - dumpsys connectivity shows expected output
Bug: 32163131
Bug: 36504926
Bug: 36988090
Bug: 38152109
Bug: 38186915
Bug: 38218697
Change-Id: I4a2129d780dfec7bca693486a100ea3c78465430