Windows: Refactor cm_Unlock*() to avoid code duplication

Windows: Refactor cm_Unlock*() to avoid code duplication

cm_Unlock() and cm_UnlockByKey() duplicate a significant amount
of code.  Refactor it into a new static function, cm_IntUnlock()
which handles the process of downgrading or releasing a file
server lock depending upon the lock state of the cm_scache_t
object.

Reviewed-on: http://gerrit.openafs.org/4923
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>
(cherry picked from commit 1ac219f537f75ac5835f750d4c9e5f4dc684c2de)

Change-Id: I4dc2a37557e3370f711f6a11743f39df6344676b
Reviewed-on: http://gerrit.openafs.org/4952
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>