diag_dns.php: Fix button icon to match text for alias actions.
diag_dns.php: Fix button icon to match text for alias actions.

NewEraCracker/pfsense,pfsense/pfsense,dennypage/pfsense,dennypage/pfsense,dennypage/pfsense,NewEraCracker/pfsense,dennypage/pfsense,NewEraCracker/pfsense,pfsense/pfsense,NewEraCracker/pfsense,pfsense/pfsense,pfsense/pfsense