[SCSI] libiscsi: add more informative failure message during iscsi scsi eh

This adds a more informative error code and message
for the iscsi scsi eh session drop paths. This allows
you to distinguish if the session was dropped due to
a connection failure vs the iscsi layer dropping
the session due to scsi eh failure processing.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>
diff --git a/include/scsi/iscsi_if.h b/include/scsi/iscsi_if.h
index a8631ac..c3e1cbc 100644
--- a/include/scsi/iscsi_if.h
+++ b/include/scsi/iscsi_if.h
@@ -263,6 +263,7 @@
 	ISCSI_ERR_INVALID_HOST		= ISCSI_ERR_BASE + 18,
 	ISCSI_ERR_XMIT_FAILED		= ISCSI_ERR_BASE + 19,
 	ISCSI_ERR_TCP_CONN_CLOSE	= ISCSI_ERR_BASE + 20,
+	ISCSI_ERR_SCSI_EH_SESSION_RST	= ISCSI_ERR_BASE + 21,
 };
 
 /*