Increase disterl buffer sizes.

At this point in riak's history disterl is our primary bottleneck.
Something about the way that it is framing small messages is causing its
tcp connection to size its send and recv buffers much smaller than
is ideal.

This change adds code to automatically set dist port sizes on nodeup,
as well as code to manually set all disterl connections to specific
sizes, meant to be used from the console for testing and tuning.