net: refactor self=this to arrow functions

Refactor unused self=this code to code without without this pattern
making it more consistent with the rest of our code.

PR-URL: https://github.com/nodejs/node/pull/5857


Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Roman Klauke <romankl@users.noreply.github.com>