When using the path to request properties, and no ZFS file system is mounted
at that path, ZFS will fall back to the parent filesystem:
> # zfs unmount myzpool/subvol-172-disk-0
> # zfs get mounted /myzpool/subvol-172-disk-0
> NAME PROPERTY VALUE SOURCE
> myzpool mounted yes -
> # zfs get mounted myzpool/subvol-172-disk-0
> NAME PROPERTY VALUE SOURCE
> myzpool/subvol-172-disk-0 mounted no -
Thus, we cannot use the path and need to use the dataset directly.
Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>