Revert "Do not install tethering in TEST_MAPPING"

This reverts commit b679b6a4.

Reason for revert:
Tethering was removed from test mapping during S development in some
branches, but is now usable gain in test mapping and needs to be part
of mainline-test-mapping testing.

Ignore-AOSP-First: Fixes difference with AOSP
Bug: 196755836
Change-Id: I1583c88257c197fa00e6c5bf273e83a70db26116
Test: TEST_MAPPING needs to be tested by treehugger