Better logging infrastructure in OffloadHardwareInterface

Test: as follows
    - built
    - flashed
    - booted
    - "runtest frameworks-net" passes
    - watch "adb shell dumpsys connectivity tethering | tail -60" shows logs
Bug: 29337859
Bug: 32163131

Merged-In: I3b178f4bb798d9ac59b366723d19e3189d39942e
Merged-In: I1b64e562c74797cbfaa26f3a1b5e38c3bf2a0c0d
Merged-In: Id0bd14e5b364c497403c2d88f7b1c31d712e6f87
Change-Id: I78f28a9e940cc7e050f2d79f877d27468d13599a