path: follow symbolic link for parent path (2)

c0e57ba9e22ee937722958d8b912ade2a37f206d fixed the fallback path.
We should do the same for name_to_handle_at().
path: make the check for unsupported name_to_handle_at symmetric

If child supports, but the parent does not, or when the child does
not support, but the parent does, assume the child is a mount point.

Only if neither supports use the fallback.