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)
{
    AssertLockNotHeld(m_total_bytes_sent_mutex);
    size_t nMessageSize = msg.data.size();
    LogPrint(BCLog::NET, "sending %s (%d bytes) peer=%d\n", msg.m_type, nMessageSize, pnode->GetId());
    if (gArgs.GetBoolArg("-capturemessages", false)) {
        CaptureMessage(pnode->addr, msg.m_type, msg.data, /*lse);
    }
    TRACE6(net, outbound_message,
        pnode->GetId(),
        pnode->m_addr_name.c_str(),
        pnode->ConnectionTypeAsString().c_str(),
        msg.m_type.c_str(),
        msg.data.size(),
        msg.data.data()
    );
     
    std::vector<unsigned char> serializedHeader;
    pnode->m_serializer->prepareForTransport(msg, serializedHeader);
    size_t nTotalSize = nMessageSize + serializedHeader.size();
    size_t nBytesSent = 0;
    {
        LOCK(pnode->cs_vSend);
        bool optimisticSend(pnode->vSendMsg.empty());
        
        pnode->mapSendBytesPerMsgType[msg.m_type] += nTotalSize;
        pnode->nSendSize += nTotalSize;
        if (pnode->nSendSize > nSendBufferMaxSize) pnode->fPauseSend = true;