Add test for tetherOffloadClient{Add, Remove, Clear} am: dad664748a am: 1dcbf69053

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/1744606

Change-Id: I537255a5acff647a8111970a8eaa44d576dbf722
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>