auth_db: doc updates for load_credentials

modules/auth_db/README

@@ -276,7 +276,7 @@ modparam("auth_db", "use_domain", 1)
      * credential = (avp_specification '=' column_name) | (column_name)
      * avp_specification = '$avp(' + 'i:'ID | 's:'NAME | alias + ')'
 
-   Default value of this parameter is "rpid".
+   Default value of this parameter is "NULL" (no credientials loaded).
 
    Example 1.8. load_credentials parameter usage
 ...

modules/auth_db/doc/auth_db_admin.xml

@@ -266,7 +266,8 @@ modparam("auth_db", "use_domain", 1)
 		</itemizedlist>
 		</para>
 		<para>
-		Default value of this parameter is <quote>rpid</quote>.
+		Default value of this parameter is <quote>NULL</quote> (no credientials
+		loaded).
 		</para>
 		<example>
 		<title><varname>load_credentials</varname> parameter usage</title>