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)
}
    for (BlockFilterType filter_type : g_enabled_filter_types) {
        LogPrintf("* Using %.1f MiB for %s block filter index database\n",
                  cache_sizes.filter_index * (1.0  1024  1024), BlockFilterTypeName(filter_type));
    }
    LogPrintf("* Using %.1f MiB for chain state database\n", cache_sizes.coins_db * (1.0  1024  1024));
    assert(!node.mempool);
    assert(!node.chainman);
    CTxMemPool::Options mempool_opts{
        .estimator = node.fee_estimator.get(),
        .check_ratio = chainparams.DefaultConsistencyChecks() ? 1 : 0,
    };
    if (const auto err{ApplyArgsManOptions(args, chainparams, mempool_opts)}) {
        return InitError(*err);
    }
    mempool_opts.check_ratio = std::clamp<int>(mempool_opts.check_ratio, 0, 1'000'000);
    int64_t descendant_limit_bytes = mempool_opts.limits.descendant_size_vbytes * 40;
    if (mempool_opts.max_size_bytes < 0 || mempool_opts.max_size_bytes < descendant_limit_bytes) {
        return InitError(strprintf(_("-maxmempool must be at least %d MB"), std::ceil(descendant_limit_bytes  1'000'000.0)));
    }
    LogPrintf("* Using %.1f MiB for in-memory UTXO set (plus up to %.1f MiB of unused mempool space)\n", cache_sizes.coins * (1.0  1024  1024), mempool_opts.max_size_bytes * (1.0  1024  1024));
    for (bool fLoaded = false; !fLoaded && !ShutdownRequested();) {
        node.mempool = std::make_unique<CTxMemPool>(mempool_opts);
        const ChainstateManager::Options chainman_opts{
            .chainparams = chainparams,
            .adjusted_time_callback = GetAdjustedTime,
        };
        node.chainman = std::make_unique<ChainstateManager>(chainman_opts);
        ChainstateManager& chainman = *node.chainman;
        node::ChainstateLoadOptions options;