tcp: Set route scope properly in cookie_v4_check().

RT_CONN_FLAGS(sk) overloads flowi4_tos with the RTO_ONLINK bit when
sk has the SOCK_LOCALROUTE flag set. This allows
ip_route_output_key_hash() to eventually adjust flowi4_scope.

Instead of relying on special handling of the RTO_ONLINK bit, we can
just set the route scope correctly. This will eventually allow to avoid
special interpretation of tos variables and to convert ->flowi4_tos to
dscp_t.
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/syncookies.c

@@ -418,8 +418,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	 * no easy way to do this.
 	 */
 	flowi4_init_output(&fl4, ireq->ir_iif, ireq->ir_mark,
-			   RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE, IPPROTO_TCP,
-			   inet_sk_flowi_flags(sk),
+			   ip_sock_rt_tos(sk), ip_sock_rt_scope(sk),
+			   IPPROTO_TCP, inet_sk_flowi_flags(sk),
 			   opt->srr ? opt->faddr : ireq->ir_rmt_addr,
 			   ireq->ir_loc_addr, th->source, th->dest, sk->sk_uid);
 	security_req_classify_flow(req, flowi4_to_flowi_common(&fl4));