NLMSG_TAIL
rta = NLMSG_TAIL(n);
memcpy(NLMSG_TAIL(n), data, len);
memset((void *) NLMSG_TAIL(n) + len, 0, NLMSG_ALIGN(len) - len);
struct rtattr *nest = NLMSG_TAIL(n);
nest->rta_len = (void *)NLMSG_TAIL(n) - (void *)nest;