MINOR: connection: Add callbacks definitions for QUIC.

The flow control at stream level is organized by types (client bidi, server bidi,
client uni, server uni). Adds at least callback to retrieve the number
of available streams by direction.
diff --git a/include/haproxy/connection-t.h b/include/haproxy/connection-t.h
index 1afae96..28dbbf4 100644
--- a/include/haproxy/connection-t.h
+++ b/include/haproxy/connection-t.h
@@ -50,6 +50,7 @@
 struct pipe;
 struct quic_conn;
 struct bind_conf;
+struct qcs;
 
 /* Note: subscribing to these events is only valid after the caller has really
  * attempted to perform the operation, and failed to proceed or complete.
@@ -421,7 +422,13 @@
 	int (*show_fd)(struct buffer *, struct connection *); /* append some data about connection into chunk for "show fd"; returns non-zero if suspicious */
 	int (*subscribe)(struct conn_stream *cs, int event_type,  struct wait_event *es); /* Subscribe <es> to events, such as "being able to send" */
 	int (*unsubscribe)(struct conn_stream *cs, int event_type,  struct wait_event *es); /* Unsubscribe <es> from events */
+	int (*ruqs_subscribe)(struct qcs *qcs, int event_type,  struct wait_event *es); /* Subscribe <es> to events, "being able to receive" only */
+	int (*ruqs_unsubscribe)(struct qcs *qcs, int event_type,  struct wait_event *es); /* Unsubscribe <es> from events */
+	int (*luqs_subscribe)(struct qcs *qcs, int event_type,  struct wait_event *es); /* Subscribe <es> to events, "being able to send" only */
+	int (*luqs_unsubscribe)(struct qcs *qcs, int event_type,  struct wait_event *es); /* Unsubscribe <es> from events */
 	int (*avail_streams)(struct connection *conn); /* Returns the number of streams still available for a connection */
+	int (*avail_streams_bidi)(struct connection *conn); /* Returns the number of bidirectional streams still available for a connection */
+	int (*avail_streams_uni)(struct connection *conn); /* Returns the number of unidirectional streams still available for a connection */
 	int (*used_streams)(struct connection *conn);  /* Returns the number of streams in use on a connection. */
 	void (*destroy)(void *ctx); /* Let the mux know one of its users left, so it may have to disappear */
 	int (*ctl)(struct connection *conn, enum mux_ctl_type mux_ctl, void *arg); /* Provides information about the mux */