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)
InitWarning(warnings);
    }
    if (!fs::is_directory(gArgs.GetBlocksDirPath())) {
        return InitError(strprintf(_("Specified blocks directory \"%s\" does not exist."), args.GetArg("-blocksdir", "")));
    }
    
    std::string blockfilterindex_value = args.GetArg("-blockfilterindex", DEFAULT_BLOCKFILTERINDEX);
    if (blockfilterindex_value == "" || blockfilterindex_value == "1") {
        g_enabled_filter_types = AllBlockFilterTypes();
    } else if (blockfilterindex_value != "0") {
        const std::vector<std::string> names = args.GetArgs("-blockfilterindex");
        for (const auto& name : names) {
            BlockFilterType filter_type;
            if (!BlockFilterTypeByName(name, filter_type)) {
                return InitError(strprintf(_("Unknown -blockfilterindex value %s."), name));
            }
            g_enabled_filter_types.insert(filter_type);
        }
    }
    
    if (args.GetBoolArg("-peerblockfilters", DEFAULT_PEERBLOCKFILTERS)) {
        if (g_enabled_filter_types.count(BlockFilterType::BASIC) != 1) {
            return InitError(_("Cannot set -peerblockfilters without -blockfilterindex."));
        }
        nLocalServices = ServiceFlags(nLocalServices | NODE_COMPACT_FILTERS);
    }
    if (args.GetIntArg("-prune", 0)) {
        if (args.GetBoolArg("-txindex", DEFAULT_TXINDEX))
            return InitError(_("Prune mode is incompatible with -txindex."));
        if (args.GetBoolArg("-reindex-chainstate", false)) {