nsenter on Alpine 3.6 won't enter namespaces for a specified PID

Steps to reproduce:
1) Start container with Alpine 3.6
2) Start a container within that container.
3) "nsenter -p -i -u -m -n -t CONTAINER_PID /bin/sh"

Expected result:
A new /bin/sh session inside of container pid.

Actual result:
nsenter shows the help display again without an error.

Command I ran:
```
/ # nsenter -m -u -i -n -p -t 46 /bin/sh
BusyBox v1.26.2 (2017-10-04 13:37:41 GMT) multi-call binary.

Usage: nsenter [OPTIONS] [PROG [ARGS]]

-t, --target=PID Target process to get namespaces from
-m, --mount[=FILE] Enter mount namespace
-u, --uts[=FILE] Enter UTS namespace (hostname etc)
-i, --ipc[=FILE] Enter System V IPC namespace
-n, --net[=FILE] Enter network namespace
-p, --pid[=FILE] Enter pid namespace
-U, --user[=FILE] Enter user namespace
-S, --setuid=UID Set uid in entered namespace
-G, --setgid=GID Set gid in entered namespace
--preserve-credentials Don't touch uids or gids
-r, --root[=DIR] Set root directory
-w, --wd[=DIR] Set working directory
-F, --no-fork Don't fork before exec'ing PROG

```

Changing the order, omitting, or even specifying the direct paths to the namespaces doesn't yield a different result.

If I run "apk add --update util-linux" then try to run the above command, I get:
`.: applet not found`

Thank you