ipv6: Specialize GETINFO address interface for v4 and v6

We require a way for the control port GETINFO address command to also return the IPv6.

We propose to specialize the interface with:

GETINFO address/v4 GETINFO address/v6

And that address alone returns the IPv4 or IPv6 if no v4 can be found which basically retain its current behavior of returning the main IPv4 address.