BUG/MEDIUM: process_stream: Don't use si_cs_io_cb() in process_stream().

Instead of using si_cs_io_cb() in process_stream()  use si_cs_send/si_cs_recv
instead, as si_cs_io_cb() may lead to process_stream being woken up when it
shouldn't be, and thus timeout would never get triggered.
diff --git a/include/proto/stream_interface.h b/include/proto/stream_interface.h
index 74537b9..4a38de8 100644
--- a/include/proto/stream_interface.h
+++ b/include/proto/stream_interface.h
@@ -53,6 +53,8 @@
 void stream_int_update_conn(struct stream_interface *si);
 void stream_int_update_applet(struct stream_interface *si);
 void stream_int_notify(struct stream_interface *si);
+int si_cs_recv(struct conn_stream *cs);
+int si_cs_send(struct conn_stream *cs);
 struct task *si_cs_io_cb(struct task *t, void *ctx, unsigned short state);
 
 /* returns the channel which receives data from this stream interface (input channel) */