Slow ops include time waiting for request body to be received

In some versions, command start time is recorded once the fixed sized header has been received, without waiting for the full request.

This means slow op logging will include time spent waiting for the request value to be received over the network.

Release notes for MB-27173 suggest this should not be the case from 5.5.0 onwards, suggesting this is a regression from the intended behaviour.

This has already been resolved in 7.0.0 by unrelated changes.