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)
m_serializer{std::make_unique<V1TransportSerializer>(V1TransportSerializer())},
      m_permission_flags{node_opts.permission_flags},
      m_sock{sock},
      m_connected{GetTime<std::chrono::seconds>()},
      addr{addrIn},
      addrBind{addrBindIn},
      m_addr_name{addrNameIn.empty() ? addr.ToStringIPPort() : addrNameIn},
      m_inbound_onion{inbound_onion},
      m_prefer_evict{node_opts.prefer_evict},
      nKeyedNetGroup{nKeyedNetGroupIn},
      id{idIn},
      nLocalHostNonce{nLocalHostNonceIn},
      m_conn_type{conn_type_in},
      m_i2p_sam_session{std::move(node_opts.i2p_sam_session)}
{
    if (inbound_onion) assert(conn_type_in == ConnectionType::INBOUND);
    for (const std::string &msg : getAllNetMessageTypes())
        mapRecvBytesPerMsgType[msg] = 0;
    mapRecvBytesPerMsgType[NET_MESSAGE_TYPE_OTHER] = 0;
    if (fLogIPs) {
        LogPrint(BCLog::NET, "Added connection to %s peer=%d\n", m_addr_name, id);
    } else {
        LogPrint(BCLog::NET, "Added connection peer=%d\n", id);
    }
}
bool CConnman::NodeFullyConnected(const CNode* pnode)
{
    return pnode && pnode->fSuccessfullyConnected && !pnode->fDisconnect;
}
void CConnman::PushMessage(CNode* pnode, CSerializedNetMsg&& msg)