#429 XNS read chunk size is to low for lhigh latency networks

[Per Johansson]

When streaming on high latency networks like DSL it is
not possible to use the full bandwidth of the network.
In my case I could not stream more the about 170 kb/s
on a link capable of 300 kb/s. This is because of the
way xstream and XNS works. By only requesting small
chunks of data (16kb) at a time the TCP windows can't
be fully used. By increasing the XNS_READ_CHUNK_SIZE
from 16kb to 64 kb I boosted the performance to about
250 kb/s. This is a workaround that increases the
performance but it doesn't solve the problem. To do
that the protocol have to be changed.

/Per Johansson