bug#48739: QEMU SSH hostfwd example from manual doesn't work anymore

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hi!

In the manual, we have an example to allow connecting to the VM via a
port forward from the host:

$(guix system vm config.scm) -nic user,model=virtio-net-pci,hostfwd=tcp::10022-:22

Unfortunately, I cannot get this to work anymore, using a very simple
operating system with following openssh-configuration:

--8<---------------cut here---------------start------------->8---
(service openssh-service-type
            (openssh-configuration
             (permit-root-login #t)
             (allow-empty-passwords? #t)
             (log-level 'debug)))
--8<---------------cut here---------------end--------------->8---

I've used port 3333 as the childhurd VM is already using 10022 by
default, like so:

$ /gnu/store/qgaihb9i6n8m96m6prrcgywwxfjyqy99-run-vm.sh -nic user,hostfwd=tcp::3333-:22

And tried connecting with:

--8<---------------cut here---------------start------------->8---
$ ssh -vvvvvv root@localhost -p3333
OpenSSH_8.6p1, OpenSSL 1.1.1j  16 Feb 2021
debug1: Reading configuration data /home/maxim/.ssh/config
debug2: checking match for 'localuser mcournoyer' host localhost originally localhost
debug3: /home/maxim/.ssh/config line 13: not matched 'localuser "maxim"' 
debug2: match not found
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts' -> '/home/maxim/.ssh/known_hosts'
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts2' -> '/home/maxim/.ssh/known_hosts2'
debug1: Authenticator provider $SSH_SK_PROVIDER did not resolve; disabling
debug2: resolving "localhost" port 3333
debug3: ssh_connect_direct: entering
debug1: Connecting to localhost [127.0.0.1] port 3333.
debug3: set_sock_tos: set socket 3 IP_TOS 0x48
debug1: Connection established.
debug1: identity file /home/maxim/.ssh/id_rsa type 0
debug1: identity file /home/maxim/.ssh/id_rsa-cert type -1
debug1: identity file /home/maxim/.ssh/id_dsa type -1
debug1: identity file /home/maxim/.ssh/id_dsa-cert type -1
debug1: identity file /home/maxim/.ssh/id_ecdsa type -1
debug1: identity file /home/maxim/.ssh/id_ecdsa-cert type -1
debug1: identity file /home/maxim/.ssh/id_ecdsa_sk type -1
debug1: identity file /home/maxim/.ssh/id_ecdsa_sk-cert type -1
debug1: identity file /home/maxim/.ssh/id_ed25519 type -1
debug1: identity file /home/maxim/.ssh/id_ed25519-cert type -1
debug1: identity file /home/maxim/.ssh/id_ed25519_sk type -1
debug1: identity file /home/maxim/.ssh/id_ed25519_sk-cert type -1
debug1: identity file /home/maxim/.ssh/id_xmss type -1
debug1: identity file /home/maxim/.ssh/id_xmss-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.6
--8<---------------cut here---------------end--------------->8---

Inside the guest, /var/log/secure doesn't show any activity so it
doesn't seem to be reached.

Am I doing something wrong?

Maxim