Don't wakeup unnecessarily in 'zpool events -f'
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 <firstname.lastname@example.org>
Reviewed-by: Tony Hutter <email@example.com>
Signed-off-by: DHE <firstname.lastname@example.org>