[SCSI] scsi_eh_prep_cmnd should save scmd->underflow

This patch (as1116) fixes a bug in scsi_eh_prep_cmnd() and
scsi_eh_restore_cmnd().  These routines are supposed to save any
values they change and restore them later, but someone forgot to
save & restore scmd->underflow.

This fixes part of the problem reported in Bugzilla #9638.

[jejb: fix up rejections around DIF/DIX]
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
diff --git a/include/scsi/scsi_eh.h b/include/scsi/scsi_eh.h
index e5499ed..06a8790 100644
--- a/include/scsi/scsi_eh.h
+++ b/include/scsi/scsi_eh.h
@@ -74,6 +74,7 @@
 	/* saved state */
 	int result;
 	enum dma_data_direction data_direction;
+	unsigned underflow;
 	unsigned char cmd_len;
 	unsigned char prot_op;
 	unsigned char *cmnd;