When ZFS aclmode is set to "passthrough" chmod(2)/fchmod(2) will result in special entries being modified in a way such that delete, delete_child, write_named_attr, write_attribute are stripped from the returned ACL entry, and the kernel / ZFS treats this as having rights equivalent to the desired POSIX mode. Historically, samba has added delete_child to the NFSv4 ACL, but this is only really called for in the case of special entries in this particular circumstance.
Alter circumstances in which delete_child is granted so that it only is added to special entries. This preserves the intend post-chmod behavior, but avoids unnecessarily increasing permissions in cases where it's not intended. Further modification of this behavior may be required so that we grant a general read or general write permissions set in case of POSIX read / POSIX write on special entries.