Let MasterSwitchPreference be restrictable

Let MasterSwitchPreference be restrictable by extending RestrictedPreference.
This is a prerequisite CL for "Hotspot & Tethering" in "Network & Internet" settings screen to be a MasterSwtichPreference.
Also changed MasterSwitchPreferenceTest perse.

Bug: 145922022
Test: SettingsRoboTests except StorageItemPreferenceControllerTest which
fails before this CL.
Change-Id: I54fa59d7adfce5f564c178c0db334974dbabf059