Add back tethering to TEST_MAPPING

Tethering was removed from test mapping during S development
in some branches, but needs to be part of mainline-test-mapping
testing.

Change-Id: I440e9ae1aa958addab1c53b441e5e9e87a6d757d
Ignore-AOSP-First: Fixes difference with AOSP
Bug: 196755836
Test: TH needs to test TEST_MAPPING config
2 files changed