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)
const CChainParams& chainparams = Params();
    auto opt_max_upload = ParseByteUnits(args.GetArg("-maxuploadtarget", DEFAULT_MAX_UPLOAD_TARGET), ByteUnit::M);
    if (!opt_max_upload) {
        return InitError(strprintf(_("Unable to parse -maxuploadtarget: '%s'"), args.GetArg("-maxuploadtarget", "")));
    }
    
    if (!CreatePidFile(args)) {
        
        return false;
    }
    if (!init::StartLogging(args)) {
        
        return false;
    }
    LogPrintf("Using at most %i automatic connections (%i file descriptors available)\n", nMaxConnections, nFD);
    
    if (args.IsArgSet("-datadir") && !args.GetPathArg("-datadir").is_absolute()) {
        LogPrintf("Warning: relative datadir option '%s' specified, which will be interpreted relative to the " 
                  "current working directory '%s'. This is fragile, because if bitcoin is started in the future "
                  "from a different location, it will be unable to locate the current data files. There could "
                  "also be data loss if bitcoin is started while in a temporary directory.\n",
                  args.GetArg("-datadir", ""), fs::PathToString(fs::current_path()));
    }
    ValidationCacheSizes validation_cache_sizes{};
    ApplyArgsManOptions(args, validation_cache_sizes);
    if (!InitSignatureCache(validation_cache_sizes.signature_cache_bytes)
        || !InitScriptExecutionCache(validation_cache_sizes.script_execution_cache_bytes))
    {
        return InitError(strprintf(_("Unable to allocate memory for -maxsigcachesize: '%s' MiB"), args.GetIntArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_BYTES >> 20)));
    }