migrate a port from one network to another but the MAC is unchanged

In telecommunication cloud, We encounter the need to migrate a port from one network to another and the port's MAC must be unchanged. After migrating, the port's attributes such as ip, gateway, route and so on should be used the new network.

  In native openstack, there is no way to do this direct, we must delete the port first and then create a new one which has the same MAC with the old port.

  So we can add the migrate port api to adapt this scene.