ddclient should support IPv6 for updates

[meyergru]

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Is your feature request related to a problem? Please describe.
I use a custom dynamic DNS update service which gets the updated IPv6 via the source of the request. In order to do that, there is an update URL ssl6.name2ip.net which resolves to an IPv6 address ONLY.

Because ddclient is not configured to use IPv6, it refuses to connect with a log message like:

12057 - [meta sequenceId="5"] WARNING: cannot connect to ssl6.name2ip.net:80 socket: IO::Socket::INET: Bad hostname 'ssl6.name2ip.net'

Describe the solution you'd like
There is a ddclient option "ipv6=yes" which should be enabled in the global configuration section to be abled to use IPv6 targets. This should either alyways be included in the ddclient.conf template or depending on a boolean option in the GUI general settings for dyndns (i.e. via a checkbox titled "use ipv6").

Describe alternatives you've considered
That could probably done in the individual sections for any service instead of the global section, but I would have expected it to work right out of the box anyway - who in their right minds disables IPv6 on purpose?

Additional context
There may be other situations where IPv6 support might come in handy.

[meyergru]

Fixed via d2798e2