Force TFTP to listen on IPv4 endpoint

On Fedora with the default configuration TFTP will listen only
on IPv6 endpoint, making imporrible for a node to reach TFTP.
This patch forces TFTP to listen on IPv4 endpoint by modifying
Xinet.d template.

Change-Id: I1ed315fae38816c8e0c2a736261d1c3736f437ff
Merge "Force TFTP to listen on IPv4 endpoint"