Users without the moderate_comments capability can no longer set the `author_ip` property directly, and instead receive a `WP_Error` if they attempt to do so. Otherwise, the `author_ip property` is populated from `$_SERVER['REMOTE_ADDR']` if present and a valid IP value. Finally, fallback to 127.0.0.1 as a last resort.
Props dd32, rachelbaker, joehoyle.
Fixes#38819.
git-svn-id: https://develop.svn.wordpress.org/trunk@39302 602fd350-edb4-49c9-b593-d223f7449a82