Enable TCP_NODELAY socket option

According to Node.JS documentation TCP_NODELAY should enabled by default for all sockets [1]. Actually, this is not true. One our user on tarantool@ noticed that he has big round-trip time (~50ms) using this driver. He sends 2 requests in sequence. First response arrives just after 1-2 ms, but second response arrives only after 40-50 ms. Adding socket.setNoDelay solved the problem at least for my tests.

1. http://nodejs.org/api/net.html#net_socket_setnodelay_nodelay