Async handler to process all incoming service invocation through XML-RPC.
This handler is executed to notify user space that a method invocation has been received and should be dispatched, returning a XmlRpcMethodResponse. This reponse (XmlRpcMethodResponse) will be used to generate a reply as fast as possible.
The method invocation, represented by this async handler, could also return a NULL value, making it possible to not reply at the moment the reply was received, but once generated the reply, the method call object (XmlRpcMethodCall) received should be used in conjuction with the method response associated (XmlRpcMethodResponse) calling to vortex_xml_rpc_notify_reply.
Previous function, vortex_xml_rpc_notify_reply, could allow to marshall the invocation into another language execution, making it easy because it is only required to marshall the method invocator received but not to have a handler inside the runtime for the other language. However, this is mainly provided to make it possible to defer the reply.