Windows: cm_BkgDaemon requeuing only applies to BkgStore

Windows: cm_BkgDaemon requeuing only applies to BkgStore

cm_BkgDaemon currently requeues failed requests for a variety
of errors.  It only applies to cm_BkgStore requests.  The current
code only supports cm_BkgStore and cm_BkgPrefetch operations.
Additional background operations may be added in the future.
If requeues are meant to apply to the new operations, they should
be explicitly specified.  Specify cm_BkgStore explicitly now.

LICENSE MIT

Change-Id: Iae7c5fe4f2f7bc701ebe93500626b68f49b0063f
Reviewed-on: http://gerrit.openafs.org/824
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>