Increasing it would have at least two benefits -

* More messages would be 'VSM' messages, so it would reduce allocation
overhead a bit.
* Remove any chance of false sharing of things that are, by design,
pushed by value onto a ypipe_t<msg_t> which is shared between two threads.

The only downside I see is slightly increased memory consumption on memory
constrained applications.

- Full discussion of this rationale is part of issue #1295