Stop tethering request only if fuzzy-matched to existing request

stopTethering with a TetheringRequest should only stop tethering if
there is an existing request (pending or serving) that fuzzy-matches the
input and whose UID matches the caller (unless the caller is Settings,
which is allowed to remove any request).

If there is no existing fuzzy-matched request, return
TETHER_ERROR_UNKNOWN_REQUEST.

Bug: 216524590
Test: atest TetheringTest RequestTrackerTest TetheringManagerTest
Change-Id: Ia8a8eab78fbecd38321fd0d48734855cff16febb
4 files changed