2976 remove useless offsetof() macros

@@ -34,20 +34,19 @@
 
 #if defined(_KERNEL) && !defined(_BOOT)
 #include <sys/varargs.h>
 #include <sys/ddi.h>
 #include <sys/sunddi.h>
+#include <sys/sysmacros.h>
 #else
 #include <stdarg.h>
 #include <stdlib.h>
 #include <string.h>
 #include <strings.h>
+#include <stddef.h>
 #endif
 
-#ifndef offsetof
-#define offsetof(s, m)          ((size_t)(&(((s *)0)->m)))
-#endif
 #define skip_whitespace(p)      while ((*(p) == ' ') || (*(p) == '\t')) p++
 
 /*
  * nvpair.c - Provides kernel & userland interfaces for manipulating
  *      name-value pairs.