Phpcs error cleanup – IpUtils class renaming (part 2)

As the last part of phpcs cleanup, we plan to rename iputils.php file to adhere to our naming standards. To increase the safety of this change the previous change only introduced the new file. This change starts using it, before the final follow-up change that will remove the old file.

https://github.com/Automattic/vip-go-mu-plugins/pull/1939