2976 remove useless offsetof() macros

*** 21,30 ****
--- 21,32 ----
  /*
   * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   */
  
+ #include <stddef.h>
+ 
  #include <sys/types.h>
  #include <sys/mdb_modapi.h>
  
  #include <sys/nsctl/nsctl.h>
  #include <sys/unistat/spcs_s.h>
*** 34,45 ****
  #include <sys/nsctl/dsw.h>
  #include <sys/nsctl/dsw_dev.h>
  
  #include <sys/nsctl/nsvers.h>
  
- #define offsetof(s, m)  ((size_t)(&((s *)0)->m))
- 
  
  const mdb_bitmask_t bi_flags_bits[] = {
          { "DSW_GOLDEN", DSW_GOLDEN, DSW_GOLDEN },
          { "DSW_COPYINGP", DSW_COPYINGP, DSW_COPYINGP },
          { "DSW_COPYINGM", DSW_COPYINGM, DSW_COPYINGM },
--- 36,45 ----