osctld: remount datasets on container stop

This is a partial workaround for openzfs/zfs#16817.
Unmounting datasets will sync dirtied pages to disk.

Author: aither64

osctld/lib/osctld/console/console.rb

@@ -98,6 +98,10 @@ def handle_ct_stop(ctrc)
 
       if ctrc.destroy_dataset_on_stop?
         GarbageCollector.free_container_run_dataset(ctrc, ctrc.dataset)
+      elsif !ct.ephemeral?
+        # Force write-out of dirtied pages
+        ct.unmount
+        ct.mount
       end
 
       ctrc.fulfil_exit