Windows: Runtime RDR Trace Toggle

Modify the IOCTL_AFS_CONFIG_LIBRARY_TRACE DeviceIoControl message
to pass an AFSDebugTraceConfigCB which is used to toggle the value
of the Library's AFSDebugTraceFnc pointer.   When the trace log is
enabled, the AFSDbgLogMsg parameter is non-NULL and when the log is
disabled, the parameter is NULL.

Change-Id: I71b951f244b760487f2ece94409cefaa7a73ea31
Reviewed-on: http://gerrit.openafs.org/9748
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Rod Widdowson <rdw@steadingsoftware.com>
Reviewed-by: Peter Scott <pscott@kerneldrivers.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>