[SCSI] fcoe,libfcoe: Move common code for fcoe_get_lesb to fcoe_transport

Except for obtaining the netdev from lport, fcoe_get_lesb is the common code
for the LLDs.

Signed-off-by: Bhanu Prakash Gollapudi <bprakash@broadcom.com>
Acked-by: Yi Zou <yi.zou@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>