[SCSI] libfc: add fcoe_fc_els_lesb to fc_fcoe.h for FC-BB-5 LESB definitions

Add struct fcoe_fc_els_lesb as described in FC-BB-5 LESB for FCoE. It has
the same size as LESB defined in FC-FS-3 (struct fc_els_lesb) but members
have different meanings according to FC-BB-5.

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>