diff/walking: enable mount manager

The default walking applier performs a real temporary mount for
unpacking, but the mount manager failed to adapt to the walking
differ.

This fixes the EROFS snapshotter together with the default walking
differ, otherwise it reports:

```
ctr: apply layer error for "[]": failed to extract layer sha256:[]:
failed to mount /var/lib/containerd/tmpmounts/containerd-mount3992073457:
internal mount option "X-containerd.mkfs.fs=ext4" was not consumed by
the mount manager
```

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

plugins/diff/walking/plugin/plugin.go

@@ -17,9 +17,12 @@
 package plugin
 
 import (
+	"errors"
+
 	"github.com/containerd/containerd/v2/core/diff"
 	"github.com/containerd/containerd/v2/core/diff/apply"
 	"github.com/containerd/containerd/v2/core/metadata"
+	"github.com/containerd/containerd/v2/core/mount"
 	"github.com/containerd/containerd/v2/plugins"
 	"github.com/containerd/containerd/v2/plugins/diff/walking"
 	"github.com/containerd/platforms"
@@ -33,6 +36,7 @@ func init() {
 		ID:   "walking",
 		Requires: []plugin.Type{
 			plugins.MetadataPlugin,
+			plugins.MountManagerPlugin,
 		},
 		InitFn: func(ic *plugin.InitContext) (any, error) {
 			md, err := ic.GetSingle(plugins.MetadataPlugin)
@@ -40,12 +44,19 @@ func init() {
 				return nil, err
 			}
 
+			var mm mount.Manager
+			if mountsI, err := ic.GetSingle(plugins.MountManagerPlugin); err == nil {
+				mm = mountsI.(mount.Manager)
+			} else if !errors.Is(err, plugin.ErrPluginNotFound) {
+				return nil, err
+			}
+
 			ic.Meta.Platforms = append(ic.Meta.Platforms, platforms.DefaultSpec())
 			cs := md.(*metadata.DB).ContentStore()
 
 			return diffPlugin{
 				Comparer: walking.NewWalkingDiff(cs),
-				Applier:  apply.NewFileSystemApplier(cs),
+				Applier:  apply.NewFileSystemApplierWithMountManager(cs, mm),
 			}, nil
 		},
 	})