net: mvneta: Use struct tc_mqprio_qopt_offload for MQPrio configuration

The struct tc_mqprio_qopt_offload is a container for struct tc_mqprio_qopt,
that allows passing extra parameters, such as traffic shaping. This commit
converts the current mqprio code to that new struct.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>