Tethering service is created after boot complete which means most of
the services are ready before tethering. Once tethering register the
callback, callback event may come-in immediately. Make sure all of
tethering related object is created, then register the callback,
receiver, or listener.
Bug: 149965121
Test: atest TetheringTests
manual on/off tethering
Change-Id: I3941a186770679e7b476073d774e2310e25e44c6