ibuf_add_n64
int ibuf_add_n64(struct ibuf *, uint64_t);
if (ibuf_add_n64(nhbuf, 0) == -1) /* set RD to 0 */
if (ibuf_add_n64(nhbuf, 0) == -1) /* set RD to 0 */
if (ibuf_add_n64(h2buf, 0) == -1) /* set RD to 0 */
if (ibuf_add_n64(h2buf, 0) == -1) /* set RD to 0 */
if (ibuf_add_n64(buf, ext) == -1)