nexthop_grp
nla_len += NETLINK_ALIGN(num_nhops * sizeof(struct nexthop_grp));
struct nexthop_grp *grp = &((struct nexthop_grp *)(nla + 1))[i];
struct nexthop_grp *grp = NLA_DATA(nla);
struct nexthop_grp *grp = NLA_DATA(attrs->nha_group);