Comment 9 for bug 2004004

Reviewed: https://review.opendev.org/c/openstack/neutron/+/872219
Committed: https://opendev.org/openstack/neutron/commit/83da1e6d79c4d971718d31cbd3aa038353adbae8
Submitter: "Zuul (22348)"
Branch: master

commit 83da1e6d79c4d971718d31cbd3aa038353adbae8
Author: Rafael Weingärtner <email address hidden>
Date: Mon Jan 30 16:10:26 2023 -0300

    Improve message for subnet gateway out of host IP addresses range

    Following the discussions on #2004004, we notice that there is an error
    message in the Neutron code that is misleading.

    This patch intends to improve the exception message, and provide a
    little bit of documentation regarding the gateway IP address
    validation for subnets.

    Related-bug: #2004004

    Change-Id: Ibf09254b5b2fee6efd3de5e5dc6f013424831db9