5045 use atomic_{inc,dec}_* instead of atomic_add_*

*** 424,434 ****
  
                  *id = handler->zi_id = inject_next_id++;
                  handler->zi_spa = spa;
                  handler->zi_record = *record;
                  list_insert_tail(&inject_handlers, handler);
!                 atomic_add_32(&zio_injection_enabled, 1);
  
                  rw_exit(&inject_lock);
          }
  
          /*
--- 424,434 ----
  
                  *id = handler->zi_id = inject_next_id++;
                  handler->zi_spa = spa;
                  handler->zi_record = *record;
                  list_insert_tail(&inject_handlers, handler);
!                 atomic_inc_32(&zio_injection_enabled);
  
                  rw_exit(&inject_lock);
          }
  
          /*
*** 501,511 ****
          list_remove(&inject_handlers, handler);
          rw_exit(&inject_lock);
  
          spa_inject_delref(handler->zi_spa);
          kmem_free(handler, sizeof (inject_handler_t));
!         atomic_add_32(&zio_injection_enabled, -1);
  
          return (0);
  }
  
  void
--- 501,511 ----
          list_remove(&inject_handlers, handler);
          rw_exit(&inject_lock);
  
          spa_inject_delref(handler->zi_spa);
          kmem_free(handler, sizeof (inject_handler_t));
!         atomic_dec_32(&zio_injection_enabled);
  
          return (0);
  }
  
  void