Updated client.js so can now pass port when bootstrapping

There is a bug in that if you want to bootstrap the client AND listen on a custom port it's impossible.

The client bootstraps and automatically starts listen as part of the bootstrap process, because no port is passed then it will listen on a random port.

Later when you go to do dht.listen then it will ignore it because it's already listening.

After the pull request you can pass the port value as part of the DHT({}); init call.