Fix checking for the feature at spa_vdev_add()

Now vdev is actually not adding if the feature is not enabled.
Previously, it was showing the error, but vdev was adding to the
pool.

The fix is to add the check at the earliest point, just after
vdev_draid_spare_create() call.

Signed-off-by: Andriy Tkachuk <andriy.tkachuk@seagate.com>

Author: andriytk

module/zfs/spa.c

@@ -7550,9 +7550,14 @@ spa_vdev_add(spa_t *spa, nvlist_t *nvroot, boolean_t check_ashift)
 	 */
 	if ((error = vdev_draid_spare_create(nvroot, vd, &ndraid,
 	    &draid_nfgroup, rvd->vdev_children)) == 0) {
+
 		if (ndraid > 0 && nvlist_lookup_nvlist_array(nvroot,
 		    ZPOOL_CONFIG_SPARES, &spares, &nspares) != 0)
 			nspares = 0;
+
+		if (draid_nfgroup > 0 && !spa_feature_is_enabled(spa,
+		    SPA_FEATURE_DRAID_FAIL_DOMAINS))
+			return (spa_vdev_exit(spa, vd, txg, ENOTSUP));
 	} else {
 		return (spa_vdev_exit(spa, vd, txg, error));
 	}
@@ -7643,10 +7648,6 @@ spa_vdev_add(spa_t *spa, nvlist_t *nvroot, boolean_t check_ashift)
 		dsl_sync_task_nowait(spa->spa_dsl_pool, spa_draid_feature_incr,
 		    (void *)(uintptr_t)ndraid, tx);
 
-		if (!spa_feature_is_enabled(spa,
-		    SPA_FEATURE_DRAID_FAIL_DOMAINS) && draid_nfgroup > 0)
-			return (spa_vdev_exit(spa, vd, txg, ENOTSUP));
-
 		if (draid_nfgroup > 0)
 			dsl_sync_task_nowait(spa->spa_dsl_pool,
 			    spa_draid_fdomains_feature_incr,