ixgbe: use correct FCoE DDP max check

Use fcoe_ddp_xid from netdev as this is correctly set for different
device IDs to avoid DDP skip error on X550 as "xid=0x20b out-of-range"

Signed-off-by: Vasu Dev <vasu.dev@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>