Just edit your tftp file for xinetd like this:
*Change the IPto be the IPof the interface you want to listen on.
To test if your tftp is available on a certain IP range use nc -u yourip 69 to see if you can still connect (/var/log/messages or /var/log/syslog) should show the connection if it is open.
Oct 13 23:20:34 01 xinetd[26631]: Started working: 1 available servic........