When using throttles with a long period, a porting issue from the JS
based throttle code meant that we'd compute a TTL in *seconds* but tell
redis that its value is in *milliseconds*, resulting in a much shorter
expiration time than desired, allowing more messages to pass the
throttling condition.
This issue doesn't apply to the redis-cell based throttle
implementation.
The fix here is simply to switch the `PX` (TTL in milliseconds) to
`EX` (TTL in seconds).
Possibly this was the source of the flakeyness that we could never
run down in https://github.com/KumoCorp/kumomta/issues/297
Wez Furlong
cd09170bc4