message: Don't assume iowait always increases on Linux
  According to [documentation] looks like this value is documented as it
  can decrease, so let's handle that without overflowing.
  [documentation]:
diff: @@ -72,7 +72,7 @@ mod imp {
  let nice = next.nice - prev.nice;
  let system = next.system - prev.system;
  let idle = next.idle - prev.idle;
  - let iowait = next.iowait - prev.iowait;
  + let iowait = next.iowait.checked_sub(prev.iowait).unwrap_or(0);
  let irq = next.irq - prev.irq;
  let softirq = next.softirq - prev.softirq;
  let steal = next.steal - prev.steal;
  