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.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>