MINOR: Add function for TX packets reference counting

Add two functions to encrement or decrement a referenc counter
attached to TX packet structure (struct quic_tx_packet). The packet are freed
when their counters reach the null value.
diff --git a/include/haproxy/xprt_quic-t.h b/include/haproxy/xprt_quic-t.h
index b5e7cad..b83c34e 100644
--- a/include/haproxy/xprt_quic-t.h
+++ b/include/haproxy/xprt_quic-t.h
@@ -482,6 +482,8 @@
 	struct quic_pktns *pktns;
 	/* Flags. */
 	unsigned int flags;
+	/* Reference counter */
+	int refcnt;
 	/* Next packet in the same datagram */
 	struct quic_tx_packet *next;
 };
diff --git a/include/haproxy/xprt_quic.h b/include/haproxy/xprt_quic.h
index 9209177..57a565b 100644
--- a/include/haproxy/xprt_quic.h
+++ b/include/haproxy/xprt_quic.h
@@ -1064,6 +1064,19 @@
 	quic_rx_packet_refdec(pkt);
 }
 
+/* Increment the reference counter of <pkt> */
+static inline void quic_tx_packet_refinc(struct quic_tx_packet *pkt)
+{
+	HA_ATOMIC_ADD(&pkt->refcnt, 1);
+}
+
+/* Decrement the reference counter of <pkt> */
+static inline void quic_tx_packet_refdec(struct quic_tx_packet *pkt)
+{
+	if (!HA_ATOMIC_SUB_FETCH(&pkt->refcnt, 1))
+		pool_free(pool_head_quic_tx_packet, pkt);
+}
+
 ssize_t quic_lstnr_dgram_read(char *buf, size_t len, void *owner,
                               struct sockaddr_storage *saddr);
 ssize_t quic_srv_dgram_read(char *buf, size_t len, void *owner,