RM7980

A commit back in may introduced filtering on "do_not_use" when selecting
IP addresses from the database. Unfortunately, this had the unintended
side-effect of applying a cartesian product to the result set, crushing
neutron DB servers in the process. This patch refactors the join to be
more sensible, as well as an inner join for safety.
Is this line needed still if we are explicitly joining in api.py?