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

*** 75,85 ****
  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);
- static int      segnf_getmemid(struct seg *seg, caddr_t addr, memid_t *memidp);
  
  
  struct seg_ops segnf_ops = {
          .dup            = segnf_dup,
          .unmap          = segnf_unmap,
--- 75,84 ----
*** 102,112 ****
          .advise         = (int (*)(struct seg *, caddr_t, size_t, uint_t))
                  segnf_nop,
          .dump           = segnf_dump,
          .pagelock       = segnf_pagelock,
          .setpagesize    = segnf_setpagesize,
-         .getmemid       = segnf_getmemid,
  };
  
  /*
   * vnode and page for the page of zeros we use for the nf mappings.
   */
--- 101,110 ----
*** 463,474 ****
  segnf_setpagesize(struct seg *seg, caddr_t addr, size_t len,
      uint_t szc)
  {
          return (ENOTSUP);
  }
- 
- /*ARGSUSED*/
- static int
- segnf_getmemid(struct seg *seg, caddr_t addr, memid_t *memidp)
- {
-         return (ENODEV);
- }
--- 461,465 ----