re #13613 rb4516 Tunables needs volatile keyword

*** 18,27 ****
--- 18,28 ----
   *
   * CDDL HEADER END
   */
  /*
   * Copyright (c) 1983, 2010, Oracle and/or its affiliates. All rights reserved.
+  * Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
   * Copyright (c) 2016, 2017 by Delphix. All rights reserved.
   */
  
  /*      Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T     */
  /*        All Rights Reserved   */
*** 133,144 ****
   * These are validated in ufs_iinit() since improper settings
   * can lead to filesystem hangs.
   */
  #define UFS_HW_DEFAULT  (16 * 1024 * 1024)
  #define UFS_LW_DEFAULT  (8 * 1024 * 1024)
! int     ufs_HW = UFS_HW_DEFAULT;
! int     ufs_LW = UFS_LW_DEFAULT;
  
  static void ihinit(void);
  extern int hash2ints(int, int);
  
  static int ufs_iget_internal(struct vfs *, ino_t, struct inode **,
--- 134,145 ----
   * These are validated in ufs_iinit() since improper settings
   * can lead to filesystem hangs.
   */
  #define UFS_HW_DEFAULT  (16 * 1024 * 1024)
  #define UFS_LW_DEFAULT  (8 * 1024 * 1024)
! volatile int    ufs_HW = UFS_HW_DEFAULT;
! volatile int    ufs_LW = UFS_LW_DEFAULT;
  
  static void ihinit(void);
  extern int hash2ints(int, int);
  
  static int ufs_iget_internal(struct vfs *, ino_t, struct inode **,