PF_AA_WHICH
snl_add_msg_attr_u32(&nw, PF_AA_WHICH, which);
snl_add_msg_attr_u32(&nw, PF_AA_WHICH, which);
snl_add_msg_attr_u32(&nw, PF_AA_WHICH, which);
{ .type = PF_AA_WHICH, .attr_name = "which", .cb = nlattr_decode_uint32 },
{ .type = PF_AA_WHICH, .off = _OUT(which), .cb = nlattr_get_uint32 },