[nrf noup] bluetooth: conn: Allow for an extra ref in bt_conn_send_cb

Allow for an additional buffer reference if callback is provided. This
can be used to extend lifetime of the net buffer until the data
transmission is confirmed by ACK of the remote.

Jira: NCSDK-27422

Signed-off-by: Marek Pieta <[email protected]>
(cherry picked from commit c735ea2)

Author: MarekPieta

subsys/bluetooth/host/conn.c

@@ -478,7 +478,11 @@ int bt_conn_send_cb(struct bt_conn *conn, struct net_buf *buf,
 	LOG_DBG("conn handle %u buf len %u cb %p user_data %p", conn->handle, buf->len, cb,
 		user_data);
 
-	if (buf->ref != 1) {
+	/* Allow for an additional buffer reference if callback is provided. This can be used to
+	 * extend lifetime of the net buffer until the data transmission is confirmed by ACK of the
+	 * remote.
+	 */
+	if (buf->ref > 1 + (cb ? 1 : 0)) {
 		/* The host may alter the buf contents when fragmenting. Higher
 		 * layers cannot expect the buf contents to stay intact. Extra
 		 * refs suggests a silent data corruption would occur if not for