[2.1] Fix IPv6 reverse hostname display on member profiles

[MegaBrutal]

Hostnames for IPv6 addresses didn't appear on member profiles because the regex to filter invalid IP values only matched for IPv4 addresses. I changed the test to the PHP filter_var() function which should be more robust.

[jdarwood007]

@MegaBrutal
Thank you for your contribution.

Do you have the related PR for SMF 3.0?

We can look at including this in a future 2.1 update, but we also need to patch it in 3.0.

[MegaBrutal]

@jdarwood007 SMF 3.0 already uses filter_var, no fix is needed there.

SMF/Sources/Actions/Profile/Summary.php

Line 107 in 4dd6381

if (Utils::$context['can_see_ip'] && empty(Config::$modSettings['disableHostnameLookup']) && filter_var(Profile::$member->formatted['ip'], FILTER_VALIDATE_IP) !== false) {