New ECHO service for all networks

[larsbrinkhoff]

Write a new server for the ECHO service on NCP socket 7, TCP port 7, Chaosnet contact ECHO. Make it work if invoked as a demon.

https://www.rfc-editor.org/rfc/rfc862.html

[larsbrinkhoff]

There already is a SYSNET;ECHO 5 for Chaosnet.