Path to control socket in DHCP4 example does not match CA example

doc/example/kea4/advanced.json uses /tmp/kea4-ctrl-socket and the config installed in /etc/kea/kea-ctrl-agent.conf uses "/tmp/kea-dhcp4-ctrl.sock.

As a result, the CA is unable to contact DHCP4 and returns misleading information: [ { "result": 1, "text": "unable to forward command to the dhcp4 service: No such file or directory. The server is likely to be offline" } ]