net: enetc: add support max frame size for tc flower offload

Base on the tc flower offload police action add max frame size by the
parameter 'mtu'. Tc flower device driver working by the IEEE 802.1Qci
stream filter can implement the max frame size filtering. Add it to the
current hardware tc flower stearm filter driver.

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