This change makes Busybox symbolically link its inbuilt utils to their
respective locations, allowing them to be invoked through their
absolute path. This means that Busybox inbuilts like e.g. `mount`
and `env` become available at `/bin/mount` and `/usr/bin/env` etc.
In particular, when entering any of the snapshot directories in
`.zfs/snapshot` (e.g. via `cd` or `ls`), ZFS normally mounts the
respective snapshot(s) on demand, using `/usr/bin/env mount [...]`
internally. Before this change, this would fail, rendering ZFS
snapshots unavailable when restoring individual files.
Signed-off-by: Max Carrara <m.carrara@proxmox.com>