tcp46 support

[Dave Cottlehuber <dch@skunkwerks.at>]

I've noticed a couple of services that I run behind spiped have a tcp46
socket open, which I'm not so familiar with. Is it possible to get
spiped to do the same thing, or do I need two daemon invocations for
each of inet/inet6? 

a go-based tool, https://github.com/hashicorp/vault  shows the
following:

vault    vault      937   7  tcp46  *:8200                *:*

In rabbitmq (written in erlang) I can use the "::" IP* address for a
tcp46 socket, however I don't know if this syntax is an erlang
convention or a standard posix/unix one, and trying it out in spiped 
only gives me an IPv6 address:

# cat /etc/rc.conf.d/spiped/riemann
  spiped_pipes="${spiped_pipes} RIEMANN"
  spiped_pipe_RIEMANN_mode="server"
  spiped_pipe_RIEMANN_source="[::]:5555"
  spiped_pipe_RIEMANN_target="127.0.0.1:12345"
  spiped_pipe_RIEMANN_key="/usr/local/etc/riemann/spiped.key"

# sockstat |grep -i spiped
  root     spiped     43908 3  tcp6   *:5555                *:*
  root     spiped     43908 4  stream -> ??
  root     spiped     43908 5  stream -> ??



https://www.rabbitmq.com/networking.html

[
  {rabbit, [
    {tcp_listeners, [{"::",       5672}]}
  ]}
].

sockstat then shows:

rabbitmq beam.smp   43118 53 tcp6   *:5672                *:*
rabbitmq beam.smp   43118 54 tcp4   *:5672                *:*

I get the same results on OSX as in FreeBSD BTW.

Thanks
Dave