MINOR: h3: implement h3 stream context

Define a new structure h3s used to provide context for a H3 stream. This
structure is allocated and stored in the qcs thanks to previous commit
which provides app-layer context storage.

For now, h3s is empty. It will soon be completed to be able to support
stateful demux : this is required to be able to demux an incomplete
frame if the rx buffer is full.
diff --git a/src/h3.c b/src/h3.c
index 459e360..2a46c1e 100644
--- a/src/h3.c
+++ b/src/h3.c
@@ -68,6 +68,11 @@
 
 DECLARE_STATIC_POOL(pool_head_h3, "h3", sizeof(struct h3));
 
+struct h3s {
+};
+
+DECLARE_STATIC_POOL(pool_head_h3s, "h3s", sizeof(struct h3s));
+
 /* Simple function to duplicate a buffer */
 static inline struct buffer h3_b_dup(struct buffer *b)
 {
@@ -720,6 +725,18 @@
 	return total;
 }
 
+static int h3_attach(struct qcs *qcs)
+{
+	struct h3s *h3s;
+
+	h3s = pool_alloc(pool_head_h3s);
+	if (!h3s)
+		return 1;
+
+	qcs->ctx = h3s;
+	return 0;
+}
+
 /* Finalize the initialization of remotely initiated uni-stream <qcs>.
  * Return 1 if succeeded, 0 if not. In this latter case, set the ->err h3 error
  * to inform the QUIC mux layer of the encountered error.
@@ -780,6 +797,13 @@
 	return 1;
 }
 
+static void h3_detach(struct qcs *qcs)
+{
+	struct h3s *h3s = qcs->ctx;
+	pool_free(pool_head_h3s, h3s);
+	qcs->ctx = NULL;
+}
+
 static int h3_finalize(void *ctx)
 {
 	struct h3 *h3 = ctx;
@@ -928,9 +952,11 @@
 /* HTTP/3 application layer operations */
 const struct qcc_app_ops h3_ops = {
 	.init        = h3_init,
+	.attach      = h3_attach,
 	.attach_ruqs = h3_attach_ruqs,
 	.decode_qcs  = h3_decode_qcs,
 	.snd_buf     = h3_snd_buf,
+	.detach      = h3_detach,
 	.finalize    = h3_finalize,
 	.is_active   = h3_is_active,
 	.release     = h3_release,