Allows to get which is the number of parameters that the given XmlRpcMethodCall object has.
The parameter number returned by this function is the one specified while calling to vortex_xml_rpc_method_call_new. It is not the number of parameter that are already added.
You should use vortex_xml_rpc_method_call_get_current_num_params to get which is the number of parameter that are added. A properly formated XmlRpcMethodCall should return the same value while calling to both function.