Expose APIs for Settings

ConnectivityManager will be a part of incoming connectivity
mainline. Settings will no longer to access the hidden methods.
For those methods that accept the interaction from users, they
should be exposed as formal interface to allow the
functionality. Expose them to API surface.

Bug: 172183305
Test: make update-api
Change-Id: Id4533b94291766bb060af0091b5ccb81a00630fd