Add TetheringServiceTest unitest

Bug: 145490751
Test: atest TetheringTests

Change-Id: Ia9e3232467c7db0e566cced84f3c72bbcd6512d6
Merged-In: I68cd403302848c041444e6d47652435d67f59273
(cherry picked from commit 790a4dd7d3aa813f15fe95c5bf3cef6dd734ce32)
4 files changed