siptrace Fix bug in documentation

The default database URL was mysql, not "", which caused me some strange issues.

modules/siptrace/README

@@ -191,7 +191,7 @@ Chapter 1. Admin Guide
 
    Database URL.
 
-   Default value is "".
+   Default value is "mysql://kamailio:kamailiorw@localhost/okamailio".
 
    Example 1.1. Set db_url parameter
 ...

modules/siptrace/doc/siptrace_admin.xml

@@ -96,7 +96,7 @@
 		</para>
 		<para>
 		<emphasis>
-			Default value is "".
+			Default value is "mysql://kamailio:kamailiorw@localhost/okamailio".
 		</emphasis>
 		</para>
 		<example>