[SCSI] iscsi: convert iser to new set/get param fns

Convert iser to libiscsi get/set param functions.
Fix bugs in it returning old error return values and
have it expose exp_statsn.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>