Using Bitcoin Core v0.15.1

I have just set `onlynet=onion` in my `bitcoin.conf` file and have the following in my logs after node restart:

    2018-02-03 12:40:52 receive version message: /Satoshi:0.15.1/: version 70015, blocks=507429, us={IPv4}:{port), peer=0
    2018-02-03 12:41:15 receive version message: /Satoshi:0.14.2/: version 70015, blocks=507429, us={IPv4}:{port), peer=2
    2018-02-03 12:41:22 receive version message: /Satoshi:0.14.2/: version 70015, blocks=507429, us={IPv4}:{port), peer=3
    2018-02-03 12:41:28 receive version message: /Satoshi:0.15.0/: version 70015, blocks=507429, us={IPv4}:{port), peer=4
    2018-02-03 12:41:57 receive version message: /Satoshi:0.15.99/: version 70015, blocks=526679, us={IPv4}:{port), peer=5
    ...
    2018-02-03 12:44:11 receive version message: /Satoshi:0.15.1/: version 70015, blocks=507429, us=[::]:0, peer=6

The peer 6 was an onion.

My `bitcoin.conf` file is as follows:

    uacomment={redacted}
    prune=10239
    banscore=10
    bantime=31536000
    maxmempool=900
    mempoolexpiry=2160
    proxy=127.0.0.1:9050
    listen=1
    bind=127.0.0.1
    onlynet=onion

All the `Used for reaching peers via` tick boxes are still ticked but disabled when I look in Options>Newtork.

Bitcoin Core should not initiate IPv4 (or IPv6) connections when `onlynet=onion`.  These connections should not be seed nodes due to low addresses:

    2018-02-03 12:40:30 Loaded 66198 addresses from peers.dat  254ms

I get some IPv4 version messages each time I restart the node.

Note: added both `dns=0` and `dnsseed=0` at the same time and this *seems* to resolve the issue with limited testing. These entries should not be necessary to limit IPv4 outgoing connect.

If people need to setup Tor for testing, the setup I have used is here on [Bitcoin.SE](https://bitcoin.stackexchange.com/a/70070/75001)
"thus it is unlikely that any Bitcoin Core peers connect to it. See "
                           "docp2p-bad-ports.md for details and a full list."),
                         prefix,
                         port);
    };
    for (const std::string& bind_arg : args.GetArgs("-bind")) {
        CService bind_addr;
        const size_t index = bind_arg.rfind('=');
        if (index == std::string::npos) {
            if (Lookup(bind_arg, bind_addr, default_bind_port, *fAllow {
                connOptions.vBinds.push_back(bind_addr);
                if (IsBadPort(bind_addr.GetPort())) {
                    InitWarning(BadPortWarning("-bind", bind_addr.GetPort()));
                }
                continue;
            }
        } else {
            const std::string network_type = bind_arg.substr(index + 1);
            if (network_type == "onion") {
                const std::string truncated_bind_arg = bind_arg.substr(0, index);
                if (Lookup(truncated_bind_arg, bind_addr, BaseParams().OnionServiceTargetPort(), false)) {
                    connOptions.onion_binds.push_back(bind_addr);
                    continue;
                }
            }
        }
        return InitError(ResolveErrMsg("bind", bind_arg));
    }
    for (const std::string& strBind : args.GetArgs("-whitebind")) {
        NetWhitebindPermissions whitebind;