doc: clearer log messages in net code samples

Code examples in documentation for net.createServer and
net.createConnection contained confusing log messages. This change makes
them clearer.

Signed-off-by: Julien Gilli <julien.gilli@joyent.com>

Cherry-picked-from: https://github.com/joyent/node/commit/8120015f4078e05ad350bb71b2839f1ce7bbc7f9