ldb_tdb: Optimise ltdb_search_and_return_base() to re-use casefolding

ldb_tdb: Optimise ltdb_search_and_return_base() to re-use casefolding

The casefolding of a DN is one of the more expensive and pointless things in LDB
operation.  The ldb_dn abstraction works hard to avoid duplicating this work, but
we can work harder to save that information.

Here we copy in the DN, that has been casefolded already for the index,
and keep that as the returned DN, after stripping any extended components.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>