Clarify IControlsTethering LOCAL_ONLY state name

Test: as follows
    - build
    - flashed
    - booted
    - "runtest frameworks-net" passes
    - manually starting tethering shows Settings and icon updates
Bug: 31466854
Bug: 32163131

Change-Id: I1f45511f00aca37480f894be4a9a004f1a3b35d7
(cherry picked from commit ca41be79)