dns: changing onelevel search for wildcard to subtree

dns: changing onelevel search for wildcard to subtree

SCOPE_ONELEVEL is used on wildcard dns searches, but onelevel searches
currently have a performance problem related to GUID indexing, so this
patch changes the search scope to SCOPE_SUBTREE.
In this case, as the onelevel and subtree sets of records are roughly
the same, and the query is matching against the DN itself, we don't
believe there's any benefit in using SCOPE_ONELEVEL over SCOPE_SUBTREE.

The onelevel performance problem will be fixed separately later, but in
the meantime this solves the DNS performance problem.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13738

Signed-off-by: Aaron Haslett <aaronhaslett@catalyst.net.nz>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
(cherry picked from commit ef379880037c10589ceeab7f985e3245817908a4)