Windows: cm_BkgFetch do not impose arbitrary timeout

Windows: cm_BkgFetch do not impose arbitrary timeout

The afs redirector will queue extent requests for the entire file
if it is being copied to local disk as long as there is enough
page cache space to store it.  If the file is 8GB and the bandwidth
from the file server is 100K/second it may take a while to get to
the end of the request queue.  Do not arbitrarily time out the
requests.

Change-Id: I12d9358ee5de37fc78d68c8e07dd14ca5dda1832
Reviewed-on: http://gerrit.openafs.org/7320
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>