ldap: the config setting for ldap_scope is 'subtree'

This doesn't really matter in the current code as it is the
default and only 'one' makes the implementation change its
scope, but for the sake of consistency let this be fixed.

src/opnsense/mvc/app/library/OPNsense/Auth/LDAP.php

@@ -88,7 +88,7 @@ class LDAP implements IAuthConnector
     /**
      * @var ldap scope
      */
-    private $ldapScope = "tree";
+    private $ldapScope = 'subtree';
 
 
     /**