forcedeth: mgmt unit interface

This patch updates the logic used to communicate with the mgmt unit. It
also adds a version check for a newer mgmt unit firmware.

* Fixed udelay to schedule_timeout_uninterruptible

Signed-off-by: Ayaz Abdulla <aabdulla@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>