Option to rely on Drupal core in detecting user IP address

Thanks for your patch, can you please convert it to MR.
And looks like your forget to update services.yml to add new argument, after adding new dependency.

Echoing #3.

Also:

+++ b/src/IPTools.php
@@ -24,11 +33,13 @@ class IPTools implements IPToolsInterface {
+      $ip_address = $this->requestStack->getCurrentRequest()->getClientIp();

This kind of magic fallback might bring some users unstuck.
If we're going to provide this option it needs to have an explicit opt-in on the settings page please, and tests.