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)
options.mempool = Assert(node.mempool.get());
        options.reindex = node::fReindex;
        options.reindex_chainstate = fReindexChainState;
        options.prune = node::fPruneMode;
        options.check_blocks = args.GetIntArg("-checkblocks", DEFAULT_CHECKBLOCKS);
        options.check_level = args.GetIntArg("-checklevel", DEFAULT_CHECKLEVEL);
        options.check_interrupt = ShutdownRequested;
        options.coins_error_cb = [] {
            uiInterface.ThreadSafeMessageBox(
                _("Error reading from database, shutting down."),
                "", CClientUIInterface::MSG_ERROR);
        };
        uiInterface.InitMessage(_("Loading block index…").translated);
        const int64_t load_block_index_start_time = GetTimeMillis();
        auto catch_exceptions = [](auto&& f) {
            try {
                return f();
            } catch (const std::exception& e) {
                LogPrintf("%s\n", e.what());
                return std::make_tuple(node::ChainstateLoadStatus::FAILURE, _("Error opening block database"));
            }
        };
        auto [status, error] = catch_exceptions([&]{ return LoadChainstate(chainman, cache_sizes, options); });
        if (status == node::ChainstateLoadStatus::SUCCESS) {
            uiInterface.InitMessage(_("Verifying blocks…").translated);
            if (chainman.m_blockman.m_have_pruned && options.check_blocks > MIN_BLOCKS_TO_KEEP) {
                LogPrintfCategory(BCLog::PRUNE, "pruned datadir may not have more than %d blocks; only checking available blocks\n",
                                  MIN_BLOCKS_TO_KEEP);
            }
            std::tie(status, error) = catch_exceptions([&]{ return VerifyLoadedChainstate(chainman, options);});