Allow to seek directly domain names in network/mx

Summary:
Ffixes the following issue:
[29-Nov-2024 20:44:49 UTC] PHP Warning: preg_match():
Delimiter must not be alphanumeric, backslash, or NUL
in /var/51-wwwroot/tools/network/mx.php on line 20

Test Plan: Search "espace-win.org" on /network/mx

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D3610