ipv4: Convert ip_mkroute_input() to dscp_t.

ipv4: Convert ip_mkroute_input() to dscp_t.

Pass a dscp_t variable to ip_mkroute_input(), instead of a plain u8, to
prevent accidental setting of ECN bits in ->flowi4_tos.

Only ip_route_input_slow() actually calls ip_mkroute_input(). Since it
already has a dscp_t variable to pass as parameter, we only need to
remove the inet_dscp_to_dsfield() conversion.

While there, reorganise the function parameters to fill up horizontal
space.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/6aa71e28f9ff681cbd70847080e1ab6b526f94f1.1728302212.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>