3006 VERIFY[S,U,P] and ASSERT[S,U,P] frequently check if first argument is zero

*** 344,354 ****
   */
  void
  spa_feature_enable(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
  {
          ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
!         VERIFY3U(0, ==, feature_do_action(spa->spa_meta_objset,
              spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
              spa->spa_feat_desc_obj, feature, FEATURE_ACTION_ENABLE, tx));
  }
  
  /*
--- 344,354 ----
   */
  void
  spa_feature_enable(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
  {
          ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
!         VERIFY0(feature_do_action(spa->spa_meta_objset,
              spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
              spa->spa_feat_desc_obj, feature, FEATURE_ACTION_ENABLE, tx));
  }
  
  /*
*** 359,369 ****
   */
  void
  spa_feature_incr(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
  {
          ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
!         VERIFY3U(0, ==, feature_do_action(spa->spa_meta_objset,
              spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
              spa->spa_feat_desc_obj, feature, FEATURE_ACTION_INCR, tx));
  }
  
  /*
--- 359,369 ----
   */
  void
  spa_feature_incr(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
  {
          ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
!         VERIFY0(feature_do_action(spa->spa_meta_objset,
              spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
              spa->spa_feat_desc_obj, feature, FEATURE_ACTION_INCR, tx));
  }
  
  /*
*** 374,384 ****
   */
  void
  spa_feature_decr(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
  {
          ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
!         VERIFY3U(0, ==, feature_do_action(spa->spa_meta_objset,
              spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
              spa->spa_feat_desc_obj, feature, FEATURE_ACTION_DECR, tx));
  }
  
  boolean_t
--- 374,384 ----
   */
  void
  spa_feature_decr(spa_t *spa, zfeature_info_t *feature, dmu_tx_t *tx)
  {
          ASSERT3U(spa_version(spa), >=, SPA_VERSION_FEATURES);
!         VERIFY0(feature_do_action(spa->spa_meta_objset,
              spa->spa_feat_for_read_obj, spa->spa_feat_for_write_obj,
              spa->spa_feat_desc_obj, feature, FEATURE_ACTION_DECR, tx));
  }
  
  boolean_t