TetherEnabler need to update tethering state of each tethering interfaces to make sure other preferences that depends on these SharedPreferences be consistent with UI. Bug: 148968321 Test: TetherEnablerTest; CodeInspectionTest. Manully test, built and flashed to crosshatch device. Change-Id: Ie0be7748adf20e6fb0ff5489795b0ca0664b6323