IFLA_PROTO_DOWN_REASON
pr = nla_nest_start(skb, IFLA_PROTO_DOWN_REASON);
[IFLA_PROTO_DOWN_REASON] = { .type = NLA_NESTED },
if (tb[IFLA_PROTO_DOWN] || tb[IFLA_PROTO_DOWN_REASON]) {
tb[IFLA_PROTO_DOWN_REASON], extack);