4171 clean up spa_feature_*() interfaces
4172 implement extensible_dataset feature for use by other zpool features
Reviewed by: Max Grossman <max.grossman@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>

@@ -248,21 +248,19 @@
                         goto out;
                 VERIFY0(bpobj_open(&dp->dp_free_bpobj,
                     dp->dp_meta_objset, obj));
         }
 
-        if (spa_feature_is_active(dp->dp_spa,
-            &spa_feature_table[SPA_FEATURE_ASYNC_DESTROY])) {
+        if (spa_feature_is_active(dp->dp_spa, SPA_FEATURE_ASYNC_DESTROY)) {
                 err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                     DMU_POOL_BPTREE_OBJ, sizeof (uint64_t), 1,
                     &dp->dp_bptree_obj);
                 if (err != 0)
                         goto out;
         }
 
-        if (spa_feature_is_active(dp->dp_spa,
-            &spa_feature_table[SPA_FEATURE_EMPTY_BPOBJ])) {
+        if (spa_feature_is_active(dp->dp_spa, SPA_FEATURE_EMPTY_BPOBJ)) {
                 err = zap_lookup(dp->dp_meta_objset, DMU_POOL_DIRECTORY_OBJECT,
                     DMU_POOL_EMPTY_BPOBJ, sizeof (uint64_t), 1,
                     &dp->dp_empty_bpobj);
                 if (err != 0)
                         goto out;