Fix IPv6

IPv6 binding, connecting, keepbody and connect command were broken. These bugs are fixed in this branch, making IPv6 networking functional.

IPv6 is enabled by default. Disable with -noipv6.

"Specify IPv4 address" was renamed to "Specify server address". This input field is long enough for a full IPv6 address in RFC 2732 notation (brackets plus port number). Beyond a certain length, the font is shrunk to fit the input, as seen below.

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The master server web view cannot contact IPv6 servers, this will be fixed in the future.