Flash Notifications: update switch state in onResume for fragment reentry

Change-Id: I9579abe65acd5b1f934575cdadc28f8e89f788a0
VanirPreferenceSwitch: add method to set/refresh switch state

previously it wasn't updating when re-entering fragments

Change-Id: I7b926603a308f7f2f2bd91e22673ffbeaa72cf59