virtio-net slow path 

There is a huge hole in the slow path (SP) area in the virtio-net driver (e.g. if_ioctl() SIOCSIFMTU does nothing).
Not only the appropriate SP code is missing, the fast path code is missing the appropriate hooks to stop/start itself which is a frequent demand as a final stage of a slow path command that changes the interface configuration like in the SIOCSIFMTU case.
