Print "Virtual IPv6 Address" on management interface queries [v4]

Add extra column to management queries for "status 2" or "status 3"
after "Virtual Address", empty if no IPv6 address assigned to this
client (or IPv6 not active at all).

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20130411150918.GW569@greenie.muc.de>
URL: http://article.gmane.org/gmane.network.openvpn.devel/7503