dbcheck: add find_missing_forward_links_from_backlinks()
find_missing_forward_links_from_backlinks() finds and returns missing forward-links by
searching all for all objects that link to the object in the backlink attribute.
This will be used in the next commit to restore forward links in a corrupted
forward link attribute by passing the missing backling objects to
err_recover_forward_links().
BUG: https://bugzilla.samba.org/show_bug.cgi?id=13228
Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Ralph Boehme <slow@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>