docs: path-lookup: update path_mountpoint() part

``nd->last_type`` to refer to the final component of the path.  It does

not call ``walk_component()`` that last time.  Handling that final

component remains for the caller to sort out. Those callers are

``path_lookupat()``, ``path_parentat()``, ``path_mountpoint()`` and

``path_lookupat()``, ``path_parentat()`` and

``path_openat()`` each of which handles the differing requirements of

different system calls.

object is wanted such as by ``stat()`` or ``chmod()``.  It essentially just

calls ``walk_component()`` on the final component through a call to

``lookup_last()``.  ``path_lookupat()`` returns just the final dentry.

``path_mountpoint()`` handles the special case of unmounting which must

not try to revalidate the mounted filesystem.  It effectively

contains, through a call to ``mountpoint_last()``, an alternate

implementation of ``lookup_slow()`` which skips that step.  This is

important when unmounting a filesystem that is inaccessible, such as

It is worth noting that when flag ``LOOKUP_MOUNTPOINT`` is set,

``path_lookupat()`` will unset LOOKUP_JUMPED in nameidata so that in the

subsequent path traversal ``d_weak_revalidate()`` won't be called.

This is important when unmounting a filesystem that is inaccessible, such as

one provided by a dead NFS server.

Finally ``path_openat()`` is used for the ``open()`` system call; it