Add stopTethering(TetheringRequest) stubs

Add a new API TetheringManager.stopTethering(TetheringRequest) to allow
apps to stop tethering for a specific request.

This CL only provides the API stubs. Implementation will be added in a
future CL.

Bug: 216524590
Test: atest TetheringManagerTest

Change-Id: If00a7dc5d328dac620fb69c384378c36e99e1856
3 files changed