Handle outgoing data streams in libvirtd

* daemon/dispatch.c: Set streamTX flag on outgoing data packets
* daemon/qemud.h: Add streamTX flag to track outgoing data
* daemon/qemud.c: Re-enable further TX when outgoing data packet
  has been fully sent.
* daemon/stream.h, daemon/stream.c: Add method for enabling TX.
  Support reading from streams and transmitting data out to client

daemon/stream.h

@@ -46,4 +46,8 @@ int
 remoteRemoveClientStream(struct qemud_client *client,
                          struct qemud_client_stream *stream);
 
+void
+remoteStreamMessageFinished(struct qemud_client *client,
+                            struct qemud_client_message *msg);
+
 #endif /* __LIBVIRTD_STREAM_H__ */