MINOR: mux-quic: factorize conn-stream attach

Provide a new function qc_attach_cs. This must be used by the app layer
when a conn-stream can be instantiated. This will simplify future
development.
diff --git a/src/h3.c b/src/h3.c
index a796845..3cce595 100644
--- a/src/h3.c
+++ b/src/h3.c
@@ -24,12 +24,11 @@
 #include <haproxy/http.h>
 #include <haproxy/htx.h>
 #include <haproxy/istbuf.h>
-#include <haproxy/mux_quic-t.h>
+#include <haproxy/mux_quic.h>
 #include <haproxy/pool.h>
 #include <haproxy/qpack-dec.h>
 #include <haproxy/qpack-enc.h>
 #include <haproxy/quic_enc.h>
-#include <haproxy/stream.h>
 #include <haproxy/tools.h>
 #include <haproxy/xprt_quic.h>
 
@@ -174,14 +173,10 @@
 	if (fin)
 		htx->flags |= HTX_FL_EOM;
 
-	cs = cs_new();
+	cs = qc_attach_cs(qcs, &htx_buf);
 	if (!cs)
 		return 1;
-	cs_attach_endp(cs, &qcs->qcc->conn->obj_type, qcs);
-
 	cs->flags |= CS_FL_NOT_FIRST;
-	cs->ctx = qcs;
-	stream_new(qcs->qcc->conn->owner, cs, &htx_buf);
 
 	/* buffer is transferred to conn_stream and set to NULL
 	 * except on stream creation error.