s3:smbd: fix interaction between chown and SD flags

s3:smbd: fix interaction between chown and SD flags

A change ownership operation that doesn't set the NT ACLs must not touch
the SD flags (type).

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13432

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Fri May 11 23:30:32 CEST 2018 on sn-devel-144

(cherry picked from commit ced55850034a3653525823bf9623912a4fcf18a0)

Autobuild-User(v4-7-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-7-test): Thu May 24 17:22:35 CEST 2018 on sn-devel-144