Add code to dump OffloadController state.

(cherry-picked from commit c2519c5f)

Bug: 29337859
Bug: 32163131
Test: observed output of "adb shell dumpsys connectivity tethering"
Change-Id: Icc5aa605cd64a4a2bb5993941dcc4010cc0b1d8e
Merged-In: Icc5aa605cd64a4a2bb5993941dcc4010cc0b1d8e