libiscsi: return new error code when nop times out

When a iscsi nop as ping timedout we were failing with the
common connection error code, ISCSI_ERR_CONN_FAILED. This
patch adds a new error code for this problem so can properly
track/distinguish in userspace.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Acked-by: Vikas Chaudhary <vikas.chaudhary@qlogic.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/include/scsi/iscsi_if.h b/include/scsi/iscsi_if.h
index fd0421c..95ed942 100644
--- a/include/scsi/iscsi_if.h
+++ b/include/scsi/iscsi_if.h
@@ -527,6 +527,7 @@
 	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,
+	ISCSI_ERR_NOP_TIMEDOUT		= ISCSI_ERR_BASE + 22,
 };
 
 /*