Settings: handle 'always ask' for SMS subscription on 3rd party apps

We need to ensure that the SMS app has a valid subscription to use as
3rd party apps don't know how to use our custom "always ask" logic.

Don't allow the user to choose "always ask" if a 3rd party SMS app is
currently the deafult.

Ticket: CYNGNOS-3068

Change-Id: I4aabf43adfb4fdc39e7656aa872abf73d9a5edbe
Signed-off-by: Roman Birg <roman@cyngn.com>