daemon/graphdriver/btrfs: use filepath.WalkDir instead of filepath.Walk

WalkDir is more performant as it doesn't perform an os.Lstat on every visited
file or directory.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/graphdriver/btrfs/btrfs.go

@@ -269,7 +269,7 @@ func subvolDelete(dirpath, name string, quotaEnabled bool) error {
 	var args C.struct_btrfs_ioctl_vol_args
 
 	// walk the btrfs subvolumes
-	walkSubvolumes := func(p string, f os.FileInfo, err error) error {
+	walkSubVolumes := func(p string, f os.DirEntry, err error) error {
 		if err != nil {
 			if os.IsNotExist(err) && p != fullPath {
 				// missing most likely because the path was a subvolume that got removed in the previous iteration
@@ -293,7 +293,7 @@ func subvolDelete(dirpath, name string, quotaEnabled bool) error {
 		}
 		return nil
 	}
-	if err := filepath.Walk(path.Join(dirpath, name), walkSubvolumes); err != nil {
+	if err := filepath.WalkDir(path.Join(dirpath, name), walkSubVolumes); err != nil {
 		return fmt.Errorf("Recursively walking subvolumes for %s failed: %v", dirpath, err)
 	}