ctdb: calculate queue input buffer size correctly

ctdb: calculate queue input buffer size correctly

The queue's input buffer is calculated in an iterative way.
This can result in a few back and forth jumping and
a few memory allocations and mem-free cycles.
This is very time consuming and not required, because the required
memory size can be calculated right away.

Signed-off-by: Swen Schillig <swen@vnet.ibm.com>
Reviewed-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Sat Aug 18 04:58:05 CEST 2018 on sn-devel-144