Allow reserved range in IP whitelist

Problem/Motivation

The IP whitelist form field currently does not validate if you try to add an IP from a reserved range, such as 127.0.0.1. I would like to be able to whitelist 127.0.0.1. My use case is that I am running end-to-end tests of the contact form on the local host (at least while testing the tests). The contact form submissions are coming from 127.0.0.1 in this case (or ::1, until I messed around with /etc/hosts a bit).

Steps to reproduce

Visit the flood control configuration form and try to add "127.0.0.1" to the IP whitelist.

Proposed resolution

Remove the FILTER_FLAG_NO_RES_RANGE from the filter_var() calls in FloodControlSettingsForm.php's validateForm().

Remaining tasks

User interface changes

None.

API changes

None.

Data model changes

None.