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 <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: DHE <git@dehacked.net>
Closes #9091

module/zfs/fm.c

@@ -683,8 +683,7 @@ zfs_zevent_wait(zfs_zevent_t *ze)
 			break;
 		}
 
-		error = cv_timedwait_sig(&zevent_cv, &zevent_lock,
-		    ddi_get_lbolt() + MSEC_TO_TICK(10));
+		error = cv_wait_sig(&zevent_cv, &zevent_lock);
 		if (signal_pending(current)) {
 			error = SET_ERROR(EINTR);
 			break;