use NULL capable segop as a shorthand for no-capabilities
Instead of forcing every segment driver to implement a dummy "return 0"
function, handle NULL capable segop function pointer as "no copabilities
supported" shorthand.

*** 131,141 ****
  static int      segvn_setpagesize(struct seg *seg, caddr_t addr, size_t len,
                      uint_t szc);
  static int      segvn_getmemid(struct seg *seg, caddr_t addr,
                      memid_t *memidp);
  static lgrp_mem_policy_info_t   *segvn_getpolicy(struct seg *, caddr_t);
- static int      segvn_capable(struct seg *seg, segcapability_t capable);
  static int      segvn_inherit(struct seg *, caddr_t, size_t, uint_t);
  
  struct  seg_ops segvn_ops = {
          .dup            = segvn_dup,
          .unmap          = segvn_unmap,
--- 131,140 ----
*** 156,166 ****
          .dump           = segvn_dump,
          .pagelock       = segvn_pagelock,
          .setpagesize    = segvn_setpagesize,
          .getmemid       = segvn_getmemid,
          .getpolicy      = segvn_getpolicy,
-         .capable        = segvn_capable,
          .inherit        = segvn_inherit,
  };
  
  /*
   * Common zfod structures, provided as a shorthand for others to use.
--- 155,164 ----
*** 9483,9499 ****
          }
  
          return (policy_info);
  }
  
- /*ARGSUSED*/
- static int
- segvn_capable(struct seg *seg, segcapability_t capability)
- {
-         return (0);
- }
- 
  /*
   * Bind text vnode segment to an amp. If we bind successfully mappings will be
   * established to per vnode mapping per lgroup amp pages instead of to vnode
   * pages. There's one amp per vnode text mapping per lgroup. Many processes
   * may share the same text replication amp. If a suitable amp doesn't already
--- 9481,9490 ----