net: Add ndo_fcoe_enable/ndo_fcoe_disable to net_device_ops

Add ndo_fcoe_enable/_disable to net_device_ops so the corresponding
HW can initialize itself for FCoE traffic or clean up after FCoE traffic is
done. This is expected to be called by the kernel FCoE stack upon receiving
a request for creating an FCoE instance on the corresponding netdev interface.
When implemented by the actual HW, the HW driver check the op code to perform
corresponding initialization or clean up for FCoE. The initialization normally
includes allocating extra queues for FCoE, setting corresponding HW registers
for FCoE, indicating FCoE offload features via netdev, etc. The clean-up would
include releasing the resources allocated for FCoE.

Signed-off-by: Yi Zou <yi.zou@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>