Don't reset notrim after low-level vdev open.

Currently, vdev_notrim is set to 0 after the actual vdev has been
opened (e.g. in vdev_disk_open()). This defeats the purpose of setting
vdev_notrim in vdev_disk_open(), so don't do it.

module/zfs/vdev.c

@@ -1214,10 +1214,8 @@ vdev_open(vdev_t *vd)
 	if (vd->vdev_ishole || vd->vdev_ops == &vdev_missing_ops)
 		return (0);
 
-	if (vd->vdev_ops->vdev_op_leaf) {
-		vd->vdev_notrim = B_FALSE;
+	if (vd->vdev_ops->vdev_op_leaf && !vd->vdev_notrim)
 		trim_map_create(vd);
-	}
 
 	for (c = 0; c < vd->vdev_children; c++) {
 		if (vd->vdev_child[c]->vdev_state != VDEV_STATE_HEALTHY) {