Fix deadlock in overlay bind

Copy up parent when binding UDS on overlayfs is supported in commit
02ab1f187c.
But the using of copyUp in overlayBind will cause sentry stuck, reason
is dead lock in renameMu.

1 [Process A] Invoke a Unix socket bind operation
  renameMu is hold in fs.(*Dirent).genericCreate by process A
2 [Process B] Invoke a read syscall on /proc/task/mounts
  waitng on Lock of renameMu in fs.(*MountNamespace).FindMount
3 [Process A] Continue Unix socket bind operation
  wating on RLock of renameMu in fs.copyUp

Root cause is recursive reading lock of reanmeMu in bind call trace,
if there are writing lock between the two reading lock, then deadlock
occured.

Fixes #1397

pkg/sentry/fs/inode_overlay.go

@@ -436,7 +436,7 @@ func overlayRename(ctx context.Context, o *overlayEntry, oldParent *Dirent, rena
 }
 
 func overlayBind(ctx context.Context, o *overlayEntry, parent *Dirent, name string, data transport.BoundEndpoint, perm FilePermissions) (*Dirent, error) {
-	if err := copyUp(ctx, parent); err != nil {
+	if err := copyUpLockedForRename(ctx, parent); err != nil {
 		return nil, err
 	}