net: ensure Socket reported address is current

Any time the connection state or the underlying handle itself changes,
the socket's name (aka, local address) can change.

To deal with this we need to reset the cached sockname any time we
set or unset the internal handle or an existing handle establishes a
connection.

PR-URL: https://github.com/nodejs/io.js/pull/2095


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>