const-ify make segment ops structures
There is no reason to keep the segment ops structures writable.

*** 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);
  
  
! struct seg_ops segnf_ops = {
          .dup            = segnf_dup,
          .unmap          = segnf_unmap,
          .free           = segnf_free,
          .fault          = (faultcode_t (*)(struct hat *, struct seg *, caddr_t,
              size_t, enum fault_type, enum seg_rw))segnf_nomap,
--- 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);
  
  
! const struct seg_ops segnf_ops = {
          .dup            = segnf_dup,
          .unmap          = segnf_unmap,
          .free           = segnf_free,
          .fault          = (faultcode_t (*)(struct hat *, struct seg *, caddr_t,
              size_t, enum fault_type, enum seg_rw))segnf_nomap,