nlmsg_reserve_data_raw
void *nlmsg_reserve_data_raw(struct nl_writer *nw, size_t sz);
#define nlmsg_reserve_object(_ns, _t) ((_t *)nlmsg_reserve_data_raw(_ns, sizeof(_t)))
#define nlmsg_reserve_data(_ns, _sz, _t) ((_t *)nlmsg_reserve_data_raw(_ns, _sz))
memcpy(nlmsg_reserve_data_raw(&nw, sizeof(nl->nl_hdr)), &nl->nl_hdr,