2883 changing "canmount" property to "on" should not always remount dataset

@@ -1446,15 +1446,17 @@
                 goto error;
         }
 
         /*
          * If the dataset's canmount property is being set to noauto,
+         * or being set to on and the dataset is already mounted,
          * then we want to prevent unmounting & remounting it.
          */
         do_prefix = !((prop == ZFS_PROP_CANMOUNT) &&
             (zprop_string_to_index(prop, propval, &idx,
-            ZFS_TYPE_DATASET) == 0) && (idx == ZFS_CANMOUNT_NOAUTO));
+            ZFS_TYPE_DATASET) == 0) && (idx == ZFS_CANMOUNT_NOAUTO ||
+            (idx == ZFS_CANMOUNT_ON && zfs_is_mounted(zhp, NULL))));
 
         if (do_prefix && (ret = changelist_prefix(cl)) != 0)
                 goto error;
 
         /*