HTTP client needs IPv6 support #1827

At a minimum, onlynet=ipv6 needs to be supported for the internal HTTP client (RPC CLI).

Indeed looks like bitcoin-cli cannot connect to IPv6 addresses, or not even parse them

$ bitcoin-cli -rpcconnect='::1' stop
error: Host not found (authoritative)
$ bitcoin-cli -rpcconnect='[::1]' stop
error: Host not found (authoritative)
$ bitcoin-cli -rpcconnect='[::1]:12345' stop
error: Host not found (authoritative)

I'm afraid to ask, but how have people always tested this stuff?

Ok ip::tcp::resolver::query defaults to address_configured which means that it will never pick a IPv6 address if IPv6 is only configured as localhost (see http://www.boost.org/doc/libs/1_55_0/doc/html/boost_asio/reference/ip__basic_resolver_query.html ).

So if you have a (non-localhost) IPv6 network set-up it should be possible to use bitcoin-cli with IPv6 addresses already.

If you don't have a non-localhost IPv6 network then it doesn't make sense to resolve any IPv6 addresses (apart from possibly localhost for testing, or specified numeric addresses?), so I think the current setting makes sense.