fcoe: add support to the get_netdev() for fcoe_interface

Adds support to fcoe_port's newly added get_netdev fucntion pointer.

Signed-off-by: Yi Zou <yi.zou@intel.com>
Cc: Bhanu Prakash Gollapudi <bprakash@broadcom.com>
Tested-by: Marcus Dennis <marcusx.e.dennis@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>