SSH sometimes doesn't listen on IPv4 0.0.0.0:1122

[cmm-cisco]

Problem traced to systemd drop-in for the ssh.socket.

https://www.freedesktop.org/software/systemd/man/latest/systemd.socket.html?__goaway_challenge=meta-refresh&__goaway_id=f5f1f710c5ccc04fc7092f5b38f23b0d&__goaway_referer=https%3A%2F%2Fwww.google.com%2F#Options

If the address string is a single number, it is read as port number to listen on via IPv6. Depending on the value of BindIPv6Only= (see below) this might result in the service being available via both IPv6 and IPv4 (default) or just via IPv6.

/usr/lib/systemd/system/ssh.socket:

…
BindIPv6Only=ipv6-only 

/usr/lib/systemd/system/ssh.socket.d/ssh.socket.conf:

[Socket]
ListenStream=
ListenStream=1122 

Should read:

[Socket]
ListenStream=
ListenStream=0.0.0.0:1122
ListenStream=[::]:1122