re #13613 rb4516 Tunables needs volatile keyword

@@ -21,10 +21,13 @@
 
 /*
  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
+/*
+ * Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
+ */
 
 /*
  * Copyright (c) 2015, Joyent, Inc. All rights reserved.
  */
 

@@ -40,11 +43,11 @@
 #endif
 
 #ifdef  _KERNEL
 
 #define _TIMER_MAX      32
-extern  int     timer_max;              /* patchable via /etc/system */
+extern  volatile int    timer_max;      /* patchable via /etc/system */
 
 /*
  * Bit values for the it_lock field.
  */
 #define ITLK_LOCKED             0x01