value shown in proc isn't the actual polling delay.  It also gives the
impression to the user that he can change the polling interval through
proc, while in fact he can't.

Also, unset passive_delay when the forced passive trip point is unbound to
allow polling to be disabled.
Signed-off-by: Frans Pop <elendil@planet.nl>
Acked-by: Matthew Garrett <mjg@redhat.com>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Len Brown <lenb@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>