PF_PT_KEY
snl_add_msg_attr(nw, PF_PT_KEY, sizeof(pool->key), &pool->key);
{ .type = PF_PT_KEY, .off = _OUT(key), .arg = (void *)sizeof(struct pf_poolhashkey), .cb = snl_attr_get_bytes },
{ .type = PF_PT_KEY, .off = _OUT(key), .arg = (void *)sizeof(struct pf_poolhashkey), .cb = nlattr_get_bytes },
nlattr_add(nw, PF_PT_KEY, sizeof(struct pf_poolhashkey), &pool->key);