By default we're not listening on an ipv6 address; so any stats sent
there just go missing. Set up by default to listen to '::' (and add
required ipv6 argument) which, thanks to dual-stack, means ipv4 & 6
packets are all accounted for.
Change-Id: I1fec03b32441a1962190f9bd8e24e8bec2318ab5