Make subscr parameter to db_subscr_get() optional

This allows to check for subscriber's presence in DB without the need to
bother with unused structure allocation.

While at it also call to db_remove_reset() and return explicitly instead
of using goto to make it a bit easier to follow the code.

Change-Id: I83b0f4a5dacb97614721690ef55bc1311624a58e
1 file changed