Add ethernet tether option into AllInOneTetherSettings

Create controller for ethernet tether preference in
AllInOneTetherSettings and corresponding test.

Test: AllInOneTetherSettingsTest; UsbTetherPreferenceControllerTest;
BluetoothTetherPreferenceControllerTest;
EthernetTetherPreferenceControllerTest;
WifiTetherDisablePreferenceControllerTest; TetherEnablerTest
Bug: 153690620

Change-Id: I8918d5c8a82c521b00eb3c712af80c2041778595