ipv4: Unmask upper DSCP bits in input route lookup

Unmask the upper DSCP bits in input route lookup so that in the future
the lookup could be performed according to the full DSCP value.

No functional changes intended since the upper DSCP bits are masked when
comparing against the TOS selectors in FIB rules and routes.
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Acked-by: Florian Westphal <fw@strlen.de>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20240821125251.1571445-9-idosch@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/route.c

@@ -2470,7 +2470,7 @@ int ip_route_input_noref(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 	struct fib_result res;
 	int err;
 
-	tos &= IPTOS_RT_MASK;
+	tos &= INET_DSCP_MASK;
 	rcu_read_lock();
 	err = ip_route_input_rcu(skb, daddr, saddr, tos, dev, &res);
 	rcu_read_unlock();