[SCSI] libiscsi_tcp: fix max_r2t manipulation

Problem description from Xi Wang:
A large max_r2t could lead to integer overflow in subsequent call to
iscsi_tcp_r2tpool_alloc(), allocating a smaller buffer than expected
and leading to out-of-bounds write.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
diff --git a/include/scsi/libiscsi.h b/include/scsi/libiscsi.h
index 2e42e9a..6e33386 100644
--- a/include/scsi/libiscsi.h
+++ b/include/scsi/libiscsi.h
@@ -268,7 +268,7 @@
 	int			lu_reset_timeout;
 	int			tgt_reset_timeout;
 	int			initial_r2t_en;
-	unsigned		max_r2t;
+	unsigned short		max_r2t;
 	int			imm_data_en;
 	unsigned		first_burst;
 	unsigned		max_burst;