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

*** 295,306 ****
  } vmu_data_t;
  
  extern struct as kas;
  extern proc_t *practive;
  extern zone_t *global_zone;
! extern struct seg_ops segvn_ops;
! extern struct seg_ops segspt_shmops;
  
  static vmu_data_t vmu_data;
  static kmem_cache_t *vmu_bound_cache;
  static kmem_cache_t *vmu_object_cache;
  
--- 295,306 ----
  } vmu_data_t;
  
  extern struct as kas;
  extern proc_t *practive;
  extern zone_t *global_zone;
! extern const struct seg_ops segvn_ops;
! extern const struct seg_ops segspt_shmops;
  
  static vmu_data_t vmu_data;
  static kmem_cache_t *vmu_bound_cache;
  static kmem_cache_t *vmu_object_cache;