MINOR: quic: Add a list to QUIC sock I/O handler RX buffer

This list will be used to store datagrams in the rxbuf struct used
by the quic_sock_fd_iocb() QUIC sock I/O handler with one rxbuf by thread.

include/haproxy/xprt_quic-t.h

@@ -616,6 +616,7 @@ struct qring {
 /* QUIC RX buffer */
 struct rxbuf {
 	struct buffer buf;
+	struct list dgrams;
 	struct mt_list mt_list;
 };
 

src/proto_quic.c

@@ -591,6 +591,7 @@ static int quic_alloc_rxbufs_listener(struct listener *l)
 			goto err;
 
 		rxbuf->buf = b_make(buf, QUIC_RX_BUFSZ, 0, 0);
+		LIST_INIT(&rxbuf->dgrams);
 		MT_LIST_APPEND(&l->rx.rxbuf_list, &rxbuf->mt_list);
 	}