rx: Big windows make us sad

rx: Big windows make us sad

The commit which took our Window size to 128 caused rxperf to run
40 times slower than before. All of the recent rx improvements have
reduced this to being around 2x slower than before, but we're still
not ready for large window sizes.

As 1.6 is nearing release, reset back to the old, fast, window size
of 32. We can revist this as further performance improvements and
restructuring happen on master.

Change-Id: Ic1de2cf33f42edaf1455b72580110d56fe968a7b
Reviewed-on: http://gerrit.openafs.org/2844
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>