use NULL dump segop as a shorthand for no-op
Instead of forcing every segment driver to implement a dummy function that
does nothing, handle NULL dump segop function pointer as a no-op shorthand.

*** 104,114 ****
  static u_offset_t segspt_shmgetoffset(struct seg *seg, caddr_t addr);
  static int segspt_shmgettype(struct seg *seg, caddr_t addr);
  static int segspt_shmgetvp(struct seg *seg, caddr_t addr, struct vnode **vpp);
  static int segspt_shmadvise(struct seg *seg, caddr_t addr, size_t len,
                          uint_t behav);
- static void segspt_shmdump(struct seg *seg);
  static int segspt_shmpagelock(struct seg *, caddr_t, size_t,
                          struct page ***, enum lock_type, enum seg_rw);
  static int segspt_shmgetmemid(struct seg *, caddr_t, memid_t *);
  static lgrp_mem_policy_info_t *segspt_shmgetpolicy(struct seg *, caddr_t);
  
--- 104,113 ----
*** 127,137 ****
          .getprot        = segspt_shmgetprot,
          .getoffset      = segspt_shmgetoffset,
          .gettype        = segspt_shmgettype,
          .getvp          = segspt_shmgetvp,
          .advise         = segspt_shmadvise,
-         .dump           = segspt_shmdump,
          .pagelock       = segspt_shmpagelock,
          .getmemid       = segspt_shmgetmemid,
          .getpolicy      = segspt_shmgetpolicy,
  };
  
--- 126,135 ----
*** 2947,2963 ****
          }
  
          return (0);
  }
  
- /*ARGSUSED*/
- void
- segspt_shmdump(struct seg *seg)
- {
-         /* no-op for ISM segment */
- }
- 
  /*
   * get a memory ID for an addr in a given segment
   */
  static int
  segspt_shmgetmemid(struct seg *seg, caddr_t addr, memid_t *memidp)
--- 2945,2954 ----