Describe the bug
Setting cupsd to listen only on socket path prevents cups daemon from starting. It worked in 2.4.8 and before and stopped working in 2.4.9.

If the only Listen directive in cupsd.conf is set to socket path like:
Listen /run/cups/cups.sock
then cupsd daemon fails to start when running from systemd:
cups.service: Failed with result 'protocol'.

The cups error log shows:
No valid Listen or Port lines were found in the configuration file.

To Reproduce
Steps to reproduce the behavior (on ArchLinux):

1. Go to /etc/cups/cupsd.conf and remove any other Listen directive than Listen /run/cups/cups.sock
2. Run systemct start cups.socket
3. Run systemctl start cups
4. See cups.service: Failed with result 'protocol'. and No valid Listen or Port lines were found in the configuration file. error messages

Expected behavior
I expect cupsd service to start like before

System Information:
OS: ArchLinux
Cups 2.4.9

Additional context
By reading changelog I presume it's somewhat related to a436956 but the listening on socket functionality is still present in cups and I don't know what users are supposed to do to make it work.