Windows: buf_RDRBuffersExist and cm_directIO

If 'cm_directIO' is true, then no RDR buffers exist.  Return immediately,
do not pass 'Go', and do not lock and walk the buffer hash table.

Reviewed-on: http://gerrit.openafs.org/9637
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit d3c04329a396cc82a71321bb209b783a1524018e)

Change-Id: I607fdb4ed1c919b805eef708be66bed60e78f423
Reviewed-on: http://gerrit.openafs.org/9648
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Windows: buf_ClearRDRFlag and cm_directIO

When 'cm_directIO' is true, there are no RDR held buffers therefore
there is nothing for buf_ClearRDRFlag() to do.  Do not pass 'Go',
do not obtain cm_scache.rw exclusive nor buf_globalLock shared.
Simply return immediately.

Reviewed-on: http://gerrit.openafs.org/9638
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 3a31f5d90c490a23b3f59f50aa9ced63b8cb98af)

Change-Id: I3d994ca361f3a512ad86b031a7a53fb381e4f241
Reviewed-on: http://gerrit.openafs.org/9649
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>