Fix blacklist unknown number mode query string.

The same was string was being used to query the database for both private and
unknown numbers, with the effect that enabling private number blocking also
blocked unknown numbers.

Change-Id: I5a77566fde3187ff6044415c64e74ce4e10cd4dc
(cherry picked from commit df77a7036ce15d9b912881a57f01728b0d0a6880)