Support IPv6 towards port-share proxy receiver

Support IPv6 towards port-share proxy receiver

While port-share already supports IPv6 connections from clients, it only
supported IPv4 connections towards the proxy receiver. The used
common/shared OpenVPN machinery is already IPv6-ready, so all needed was
to use properly-sized `sockaddr` structs and removing hardcoded IPv4
restrictions.

Signed-off-by: Corubba Smith <corubba@gmx.de>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <dcc7e538-2035-4697-b306-10eb470632f3@gmx.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg30115.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>