ZED can prevent CPU's from properly sleeping.
Rather than periodically waking up in the zevents code, just go to sleep and wait for a wakeup.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: DHE <git@dehacked.net>
Closes#9091