s3:modules:zfsacl/ixnas - fix SD control flags

PR: https://github.com/freenas/ports/pull/950

Investigation of control flags set in Windows security descriptors
in various circumstances indicates that SEC_DESC_DACL_AUTO_INHERITED
is set on directories even when auto-inheritance is disabled
(has PAI in SDDL output). Internally in samba this flag is expected
to be present in se_create_child_secdesc() otherwise ACE_INHERITED_ACE
will be stripped from the resulting child security descriptor. Primary
caller of this is inherit_new_acl() in source3/smbd/open.c, but there
is no guarantee that this won't be used in other places in Samba and so
it's important that the generic secdesc function return something
sensible. Impact on Windows clients is unknown, but no issues have been
observed in the wild.