ixgbe: Add infrastructure code for FCoE large receive offload to 82599

This adds infrastructure code for FCoE Rx side offload feature to
82599, which provides large receive offload for FCoE by Direct
Data Placement (DDP). The ixgbe_fcoe_ddp_get() and ixgbe_fcoe_ddp_put()
pair corresponds to the netdev support to FCoE by the function pointers
provided in net_device_ops as ndo_fcoe_ddp_setup and ndo_fcoe_ddp_done.
The implementation of these in ixgbe is shown in the next patch.

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