add and incorporate TetheringConfiguration.dump()

Test: as follows
    - built (bullhead)
    - flashed
    - booted
    - "runtest frameworks-net" passes
    - "adb shell dumpsys connectivity" shows expected output
Bug: 36216864
Change-Id: I2b34bdd286e9b04ffaa5f7d28f3befa0c31a0f5b