s3-winbind: Fix memory leak with each cached credential login

s3-winbind: Fix memory leak with each cached credential login

When we allow offline logon and have a lot of logins, windbind will leak
4k of memory which each log in. On systems with heavy load this can grow
quickly and the OOM killer will kill Winbind.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11999

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Wed Jun 29 19:03:53 CEST 2016 on sn-devel-144