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)
if (args.GetBoolArg("-reindex-chainstate", false)) {
        
        if (args.GetBoolArg("-coinstatsindex", DEFAULT_COINSTATSINDEX)) {
            return InitError(_("-reindex-chainstate option is not compatible with -coinstatsindex. Please temporarily disable coinstatsindex while using -reindex-chainstate, or replace -reindex-chainstate with -reindex to fully rebuild all indexes."));
        }
        if (g_enabled_filter_types.count(BlockFilterType::BASIC)) {
            return InitError(_("-reindex-chainstate option is not compatible with -blockfilterindex. Please temporarily disable blockfilterindex while using -reindex-chainstate, or replace -reindex-chainstate with -reindex to fully rebuild all indexes."));
        }
        if (args.GetBoolArg("-txindex", DEFAULT_TXINDEX)) {
            return InitError(_("-reindex-chainstate option is not compatible with -txindex. Please temporarily disable txindex while using -reindex-chainstate, or replace -reindex-chainstate with -reindex to fully rebuild all indexes."));
        }
    }
#if defined(USE_SYSCALL_SANDBOX)
    if (args.IsArgSet("-sandbox") && !args.IsArgNegated("-sandbox")) {
        const std::string sandbox_arg{args.GetArg("-sandbox", "")};
        bool log_syscall_violation_before_terminating{false};
        if (sandbox_arg == "log-and-abort") {
            log_syscall_violation_before_terminating = true;
        } else if (sandbox_arg == "abort") {
            
        } else {
            return InitError(Untranslated("Unknown syscall sandbox mode (-sandbox=<mode>). Available modes are \"log-and-abort\" and \"abort\"."));
        }
        
        const std::vector<std::string> features_using_execve{
            "-alertnotify",
            "-blocknotify",
            "-signer",
            "-startupnotify",
            "-walletnotify",