In the config file for xinetd, you can specify the interface to offer service by the attribute:
Answer: bind
Explanation:
From the man pages:
bind Allows a service to be bound to a specific interface on the machine. This means you can have a telnet server listening on a local, secured interface, and not on the external interface. Or one port on one interface can do something, while the same port on a different interface can do something completely different.