ldb-samba:ldif_handlers: dn_link_comparison semi-sorts deleted objects

ldb-samba:ldif_handlers: dn_link_comparison semi-sorts deleted objects

We were always returning -1 for a deleted object, which works for an
equality test, but not a relative comparison.

This sorts deleted DNs toward the end of the list -- except when both
DNs are deleted. What should happen there is yet to be determined.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15625

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
(cherry picked from commit db963b1674ede357d4edba578e0e0372dcb2f287)