ixgbe: Add support for the net_device_ops.ndo_fcoe_enable/disable to 82599

This adds support to the net_device_ops.ndo_fcoe_enable/disable for 82599. This
consequently allows us to dynamically turn FCoE offload feature on or off
upon incoming calls to ndo_fcoe_enable/disable. When this happens, FCoE offload
features are enabled/disabled accordingly, and this is regardless of whether
DCB being turned on or not.

Signed-off-by: Yi Zou <yi.zou@intel.com>
Acked-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>