nvlist_unpack_header
ptr = nvlist_unpack_header(nvl, ptr, nfds, &isbe, &left);
ptr = nvlist_unpack_header(nvl, ptr, nfds,
ptr = nvlist_unpack_header(tmpnvl, ptr, nfds, &isbe,
const unsigned char *nvlist_unpack_header(nvlist_t *nvl,