Add boot_hrtime to global and zone kstats.

*** 22,31 ****
--- 22,32 ----
  /*        All Rights Reserved   */
  
  /*
   * Copyright (c) 1988, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright (c) 2013, Joyent, Inc.  All rights reserved.
+  * Copyright 2016 Garrett D'Amore
   */
  
  #include <sys/param.h>
  #include <sys/t_lock.h>
  #include <sys/types.h>
*** 312,321 ****
--- 313,323 ----
  static int fsflushcnt;  /* counter for t_fsflushr */
  int     dosynctodr = 1; /* patchable; enable/disable sync to TOD chip */
  int     tod_needsync = 0;       /* need to sync tod chip with software time */
  static int tod_broken = 0;      /* clock chip doesn't work */
  time_t  boot_time = 0;          /* Boot time in seconds since 1970 */
+ hrtime_t boot_hrtime = 0;       /* gethrtime() at boot */
  cyclic_id_t clock_cyclic;       /* clock()'s cyclic_id */
  cyclic_id_t deadman_cyclic;     /* deadman()'s cyclic_id */
  
  extern void     clock_tick_schedule(int);
  
*** 1901,1910 ****
--- 1903,1915 ----
  
          if (!boot_time) {
                  boot_time = ts.tv_sec;
                  set_clock = 1;
          }
+         if (!boot_hrtime) {
+                 boot_hrtime = gethrtime();
+         }
  
          if (set_clock)
                  set_hrestime(&ts);
  
          mutex_exit(&tod_lock);