ipv6 and dual stack support

[Vlad118]

Fixes #139 where servers using ipv6 addresses and ipv6 domain names are unreachable.

• The bridge is made to match the outbound socket to IPv4 or IPv6, previously only IPv4.
• The server listener is set to IPv6 and socket2 dependency is used to disable set_only_v6 flag (enabled by default for Windows, but allegedly not for Linux, which is why we need to use this extra dependency which exposes this flag in socket).
• uPnP restricted to IPv4 only.

[Vlad118]

Note: IPv4 addresses are sanitised on lua side to automatically add the server port if omitting it, by checking if a colon : exists or not i.e. <ipv4_addr>:<port>. But as ipv6 addresses naturally contain colons, this does not work, so you need to type the port at the end of an ipv6 address. This could be fixed with a more intelligent regex to capture both ipv4 and ipv6 addresses and domains