NL_ITEM_ALIGN
#define NLMSG_ALIGN(_len) NL_ITEM_ALIGN(_len)
#define NLA_ALIGN(_len) NL_ITEM_ALIGN(_len)
#define GENL_HDRLEN NL_ITEM_ALIGN(sizeof(struct genlmsghdr))
sizeof(ifindex) + NL_ITEM_ALIGN(ifname_len + 1);
#define NL_RTA_ALIGN NL_ITEM_ALIGN
#define RTNH_ALIGN(_len) NL_ITEM_ALIGN(_len)
len = NL_ITEM_ALIGN(rtnh->rtnh_len);