MINOR: connection: introduce conn_stream

This patch introduces a new struct conn_stream. It's the stream-side of
a multiplexed connection. A pool is created and destroyed on exit. For
now the conn_streams are not used at all.
diff --git a/include/proto/obj_type.h b/include/proto/obj_type.h
index 60265b5..617464c 100644
--- a/include/proto/obj_type.h
+++ b/include/proto/obj_type.h
@@ -119,6 +119,18 @@
 	return __objt_appctx(t);
 }
 
+static inline struct conn_stream *__objt_cs(enum obj_type *t)
+{
+	return (container_of(t, struct conn_stream, obj_type));
+}
+
+static inline struct conn_stream *objt_cs(enum obj_type *t)
+{
+	if (!t || *t != OBJ_TYPE_CS)
+		return NULL;
+	return __objt_cs(t);
+}
+
 static inline struct connection *__objt_conn(enum obj_type *t)
 {
 	return container_of(t, struct connection, obj_type);
@@ -152,6 +164,7 @@
 	case OBJ_TYPE_APPLET:   return __objt_applet(t);
 	case OBJ_TYPE_APPCTX:   return __objt_appctx(t);
 	case OBJ_TYPE_CONN:     return __objt_conn(t);
+	case OBJ_TYPE_CS:       return __objt_cs(t);
 	default:                return NULL;
 	}
 }