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)
threadDNSAddressSeed = std::thread(&util::TraceThread, "dnsseed", [this] { ThreadDNSAddressSeed(); });
     
    threadOpenAddedConnections = std::thread(&util::TraceThread, "addcon", [this] { ThreadOpenAddedConnections(); });
    if (connOptions.m_use_addrman_outgoing && !connOptions.m_specified_outgoing.empty()) {
        if (m_client_interface) {
            m_client_interface->ThreadSafeMessageBox(
                _("Cannot provide specific connections and have addrman find outgoing connections at the same time."),
                "", CClientUIInterface::MSG_ERROR);
        }
        return false;
    }
    if (connOptions.m_use_addrman_outgoing || !connOptions.m_specified_outgoing.empty()) {
        threadOpenConnections = std::thread(
            &util::TraceThread, "opencon",
            [this, connect = connOptions.m_specified_outgoing] { ThreadOpenConnections(connect); });
    }
     
    threadMessageHandler = std::thread(&util::TraceThread, "msghand", [this] { ThreadMessageHandler(); });
    if (m_i2p_sam_session) {
        threadI2PAcceptIncoming =
            std::thread(&util::TraceThread, "i2paccept", [this] { ThreadI2PAcceptIncoming(); });
    }
     
    scheduler.scheduleEvery([this] { DumpAddresses(); }, DUMP_PEERS_INTERVAL);
    return true;
}
class CNetCleanup
{
public:
    CNetCleanup() = default;