You have declared an XA data source. Such a data source does not use the connection-url tag. If you don't need an XA data source, use local-tx-datasource and it will read the connection-url tag. If you need an XA data source, you should pass a xa-datasource-property that sets the port. You'll have to read the Derby docs to find out what property to set.
The property to set is 'portNumber'. You can also set 'serverName' if it's a remote host (default appears to be localhost). I didn't see any error/warning message about connection-url being wrong or ignored but that would have been handy :-)