ipv6 support for client configuration

[campbellbs]

IPv6 for client configuration is now possible with or without specific port. Different configurations were tested manually, e.g.:

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[foux]

Any reason this can't be merged? Thanks

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[systemcrash]

I don't see the advantage to use an obscure library to verify an IPv6 address when one can simply use the net library and parse an address that way. It's more resilient and more widely used. Plus the various cases of the form "host:port", "host%zone:port", "[host]:port" or "[host%zone]:port" into host or host%zone and port don't all seem covered here.

There are also potentially cases when the IPv6::ffff:IPv4 forms may also arise.

[Neustradamus]

@ngoduykhanh: What do you think?

[systemcrash]

Just test ipv6/4 using an OS library. There are a bunch of weird pathological cases accounted for there that naive test cases miss.

I