use NULL setpagesize segop as a shorthand for ENOTSUP
Instead of forcing every segment driver to implement a dummp function to
return (hopefully) ENOTSUP, handle NULL setpagesize segop function pointer
as "return ENOTSUP" shorthand.

@@ -2004,11 +2004,12 @@
 }
 
 int
 segop_setpagesize(struct seg *seg, caddr_t addr, size_t len, uint_t szc)
 {
-        VERIFY3P(seg->s_ops->setpagesize, !=, NULL);
+        if (seg->s_ops->setpagesize == NULL)
+                return (ENOTSUP);
 
         return (seg->s_ops->setpagesize(seg, addr, len, szc));
 }
 
 int