Additional functionality for rxperf

Additional functionality for rxperf

Add the ability to initiate multiple pthread threads issuing
calls on the same connection to the server.

Add ability to set max window size.

Add ability to adjust min peer timeout.

Reviewed-on: http://gerrit.openafs.org/2835
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 9a6dca070733dd5065c37cd044a3d2ded2268b14)
Change-Id: Ifeb786f3f7bf2433ff6f5729773a7e4794511cd6
Reviewed-on: http://gerrit.openafs.org/2917