vlan: Add support to netdev_ops.ndo_fcoe_get_wwn for VLAN device

Implements the netdev_ops.ndo_fcoe_get_wwn for VLAN device.

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>