XML-RPC server: Add IPv6 support

SimpleXMLRPCServer uses AF_INET as default address family.
This means it can only bind to IPv4 addresses.

GlancesXMLRPCServer is a wrapper class that makes it able to listen on
IPv6 connections.
The AF_INET or AF_INET6 address family ìs now determined by
socket.getaddrinfo() automatically.
This way the code is independent from the stack IP version.