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)
LOCK(m_nodes_mutex);
            CNode* pnode = FindNode(static_cast<CService>(addrConnect));
            if (pnode) {
                LogPrintf("Failed to open new connection, already connected\n");
                return nullptr;
            }
        }
    }
    
    bool connected = false;
    std::unique_ptr<Sock> sock;
    Proxy proxy;
    CAddress addr_bind;
    assert(!addr_bind.IsValid());
    std::unique_ptr<i2p::sam::Session> i2p_transient_session;
    if (addrConnect.IsValid()) {
        const bool use_proxy{GetProxy(addrConnect.GetNetwork(), proxy)};
        bool proxyConnectionFailed = false;
        if (addrConnect.GetNetwork() == NET_I2P && use_proxy) {
            i2p::Connection conn;
            if (m_i2p_sam_session) {
                connected = m_i2p_sam_session->Connect(addrConnect, conn, proxyConnectionFailed);
            } else {
                i2p_transient_session = std::make_unique<i2p::sam::Session>(proxy.proxy, &interruptNet);
                connected = i2p_transient_session->Connect(addrConnect, conn, proxyConnectionFailed);
            }
            if (connected) {
                sock = std::move(conn.sock);