Added slave->ttl - time to live for the registered slave.
When slave was not found we will not remove it immediately but wait until ->ttl attempts were done.
It prevents various debouncing effects(problems with pull-up, power).
Signed-off-by: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>