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.

*** 73,84 ****
  static int      segnf_gettype(struct seg *seg, caddr_t addr);
  static int      segnf_getvp(struct seg *seg, caddr_t addr, struct vnode **vpp);
  static void     segnf_dump(struct seg *seg);
  static int      segnf_pagelock(struct seg *seg, caddr_t addr, size_t len,
                      struct page ***ppp, enum lock_type type, enum seg_rw rw);
- static int      segnf_setpagesize(struct seg *seg, caddr_t addr, size_t len,
-                     uint_t szc);
  
  
  struct seg_ops segnf_ops = {
          .dup            = segnf_dup,
          .unmap          = segnf_unmap,
--- 73,82 ----
*** 100,110 ****
          .getvp          = segnf_getvp,
          .advise         = (int (*)(struct seg *, caddr_t, size_t, uint_t))
                  segnf_nop,
          .dump           = segnf_dump,
          .pagelock       = segnf_pagelock,
-         .setpagesize    = segnf_setpagesize,
  };
  
  /*
   * vnode and page for the page of zeros we use for the nf mappings.
   */
--- 98,107 ----
*** 453,465 ****
  segnf_pagelock(struct seg *seg, caddr_t addr, size_t len,
      struct page ***ppp, enum lock_type type, enum seg_rw rw)
  {
          return (ENOTSUP);
  }
- 
- /*ARGSUSED*/
- static int
- segnf_setpagesize(struct seg *seg, caddr_t addr, size_t len,
-     uint_t szc)
- {
-         return (ENOTSUP);
- }
--- 450,454 ----