ZFS: inherited `mountpoint=legacy` is not considered for `zfs_fs`

[nativerv]

Properties of parent dataset in ZFS are inherited by children. When a dataset has options.mountpoint = "legacy";, it's children are legacy too, but disko incorrectly uses -o zfsutil/zfs mount on them (it considers only self options.mountpoint from each zfs_fs, which is a workaround currently, but causes repetition):

+ mount pool/docker /mnt/var/lib/docker -o X-mount.mkdir -o defaults -o zfsutil -t zfs
filesystem 'pool/docker' cannot be mounted using 'zfs mount'.
Use 'zfs set mountpoint=/mnt/var/lib/docker' or 'mount -t zfs pool/docker /mnt/var/lib/docker'.
See zfs(8) for more information.
+ rm -rf /tmp/tmp.0BAzCacaid