ldb: bump version of the required system ldb to 1.1.24

ldb: bump version of the required system ldb to 1.1.24

This is needed to ensure we build against a system ldb library that
contains the fixes for CVE-2015-5330 and CVE-2015-3223.

autobuild must still be able to build against the older version
1.1.17 including the patches.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=11325
Bug: https://bugzilla.samba.org/show_bug.cgi?id=11599
Bug: https://bugzilla.samba.org/show_bug.cgi?id=11636

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>