2976 remove useless offsetof() macros

*** 27,36 ****
--- 27,37 ----
  #include <sys/ksynch.h>
  #include <sys/cmn_err.h>
  #include <sys/kmem.h>
  #include <sys/conf.h>
  #include <sys/errno.h>
+ #include <sys/sysmacros.h>
  
  #ifdef _SunOS_5_6
  /*
   * on 2.6 both dki_lock.h and rpc/types.h define bool_t so we
   * define enum_t here as it is all we need from rpc/types.h
*** 5637,5653 ****
          mutex_exit(&rdc_conf_lock);
  
          return (rc);
  }
  
- /*
-  * Yet another standard thing that is not standard ...
-  */
- #ifndef offsetof
- #define offsetof(s, m)  ((size_t)(&((s *)0)->m))
- #endif
- 
  static int
  rdc_status(void *arg, int mode, rdc_config_t *uparms, spcs_s_info_t kstatus)
  {
          rdc_k_info_t *krdc;
          rdc_u_info_t *urdc;
--- 5638,5647 ----