[SCSI] fcoe, libfc: add get_lesb() to allow LLD to fill the link error status block (LESB)

Add a member function pointer as get_lesb to libfc_function_template so LLD
can fill the LESB based on its own statistics. For fcoe, it fills the LESB
as a fcoe_fc_els_lesb struct 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>