SSH not working when not running in superpowered mode

**Image I'm using:** The official Bottlerocket v0.9.3 admin container image on a metal-dev variant on aarch64.

**Issue or Feature Request:** When not running the admin container in superpowered mode (user data `superpowered = false`), I cannot connect to it via SSH.

**Initial Notes**:

* SSH access without being superpowered used to work in v0.8.0, before the move to systemd.
* Looking at the host via the serial console, `host-containers@admin.service` is reported as active/running and the unit's journal contains no errors. However, `sshd` is nowhere to be found in the list of processes.
* Attaching strace to systemd, it appears comatose (`ppoll(NULL, 0, NULL, NULL, 0)`; waiting on an empty set of file descriptors without a timeout; unless it's an idiom I'm not familiar with, this seems unhealthy).
* I can enter the admin container via the control container and start `sshd` manually in a session there. I can then connect via SSH as I expected to.