Windows: do not return STATUS_RETRY for rx timeouts

Report the RPC server unavailable instead.

Change-Id: I9a6d8eec9d93f66b098b2edc4119d2e759efd9a1
Reviewed-on: http://gerrit.openafs.org/10150
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>