ipv4: Unmask upper DSCP bits in __ip_queue_xmit()

The function is passed the full DS field in its 'tos' argument by its
two callers. It then masks the upper DSCP bits using RT_TOS() when
passing it to ip_route_output_ports().

Unmask the upper DSCP bits when passing 'tos' to ip_route_output_ports()
so that in the future it could perform the FIB lookup according to the
full DSCP value.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20240903135327.2810535-2-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/ip_output.c

@@ -494,7 +494,7 @@ int __ip_queue_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl,
 					   inet->inet_dport,
 					   inet->inet_sport,
 					   sk->sk_protocol,
-					   RT_TOS(tos),
+					   tos & INET_DSCP_MASK,
 					   sk->sk_bound_dev_if);
 		if (IS_ERR(rt))
 			goto no_route;