no-op: Use helper class to handle pending requests

Pending requests should be updated via a helper class RequestTracker
and stored in a Request wrapper object. This will help out with future
changes to associate each TetheringRequest with it's own
IIntResultListener and make it easier to gate behavior changes.

Bug: 216524590
Test: atest TetheringTest RequestTrackerTest
Change-Id: Ib867e91863bdf618bb0e955eeb529cd132209d77
6 files changed