[SCSI] fcoe: Fix using VLAN ID in creating lport's WWWN/WWPN

If the underlying netdev is a VLAN device, make sure the VLAN ID is integrated
into the WWNN/WWPN name generation. Also added/updated the comments to reflect
this change.

Signed-off-by: Yi Zou <yi.zou@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>