no get_link() anymore. we have step_into() and pick_link().

walk_component() will call step_into(), in turn call pick_link,
and return symlink name.
Signed-off-by: Fox Chen <foxhlchen@gmail.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Link: https://lore.kernel.org/r/20210527091618.287093-10-foxhlchen@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>