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)
uint64_t nonce = GetDeterministicRandomizer(RANDOMIZER_ID_LOCALHOSTNONCE).Write(id).Finalize();
    ServiceFlags nodeServices = nLocalServices;
    if (NetPermissions::HasFlag(permission_flags, NetPermissionFlags::BloomFilter)) {
        nodeServices = static_cast<ServiceFlags>(nodeServices | NODE_BLOOM);
    }
    const bool inbound_onion = std::find(m_onion_binds.begin(), m_onion_binds.end(), addr_bind) != m_onion_binds.end();
    CNode* pnode = new CNode(id,
                             std::move(sock),
                             addr,
                             CalculateKeyedNetGroup(addr),
                             nonce,
                             addr_bind,
                             "",
                             ConnectionType::INBOUND,
                             inbound_onion,
                             CNodeOptions{
                               .permission_flags = permission_flags,
                               .prefer_evict = discouraged,
                             });
    pnode->AddRef();
    m_msgproc->InitializeNode(*pnode, nodeServices);
    LogPrint(BCLog::NET, "connection from %s accepted\n", addr.ToString());
    {
        LOCK(m_nodes_mutex);
        m_nodes.push_back(pnode);
    }
    
    RandAddEvent((uint32_t)id);
}
bool CConnman::AddConnection(const std::string& address, ConnectionType conn_type)