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

*** 97,107 ****
          size_t          softlockcnt;
          domid_t         domid;
          segmf_map_t     *map;
  };
  
! static struct seg_ops segmf_ops;
  
  static int segmf_fault_gref_range(struct seg *seg, caddr_t addr, size_t len);
  
  static struct segmf_data *
  segmf_data_zalloc(struct seg *seg)
--- 97,107 ----
          size_t          softlockcnt;
          domid_t         domid;
          segmf_map_t     *map;
  };
  
! static const struct seg_ops segmf_ops;
  
  static int segmf_fault_gref_range(struct seg *seg, caddr_t addr, size_t len);
  
  static struct segmf_data *
  segmf_data_zalloc(struct seg *seg)
*** 734,744 ****
          }
  
          return (0);
  }
  
! static struct seg_ops segmf_ops = {
          .dup            = segmf_dup,
          .unmap          = segmf_unmap,
          .free           = segmf_free,
          .fault          = segmf_fault,
          .faulta         = segmf_faulta,
--- 734,744 ----
          }
  
          return (0);
  }
  
! static const struct seg_ops segmf_ops = {
          .dup            = segmf_dup,
          .unmap          = segmf_unmap,
          .free           = segmf_free,
          .fault          = segmf_fault,
          .faulta         = segmf_faulta,