net: qos: add tc police offloading action with max frame size limit

Current police offloading support the 'burst'' and 'rate_bytes_ps'. Some
hardware own the capability to limit the frame size. If the frame size
larger than the setting, the frame would be dropped. For the police
action itself already accept the 'mtu' parameter in tc command. But not
extend to tc flower offloading. So extend 'mtu' to tc flower offloading.

Signed-off-by: Po Liu <Po.Liu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>