[SCSI] fcoe: move netdev to fcoe_interface

The network interface needs to be shared between all NPIV VN_Ports, therefor
it should be tracked in the fcoe_interface and not for each SCSI host in
fcoe_port.

Signed-off-by: Chris Leech <christopher.leech@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>