parse_flow_nlattrs
err = parse_flow_nlattrs(attr, a, &attrs, log);
err = parse_flow_nlattrs(encap, a, key_attrs, log);
err = parse_flow_nlattrs(nla_key, a, &key_attrs, log);
int parse_flow_nlattrs(const struct nlattr *attr, const struct nlattr *a[],