Defaults to 2000 only if connectionTimeout is not a number
Defaults to 2000 only if connectionTimeout is not a number

This allows to set connectionTimeout as 0 disabling the node.js idle timeout (https://nodejs.org/api/net.html#net_socket_settimeout_timeout_callback). The socket will then use the kernel default timeout (issue #161)

mongodb/node-mongodb-native,mongodb/node-mongodb-native,mongodb/node-mongodb-native,mongodb/node-mongodb-native