Windows: NPCancelConnection set correct length

Windows: NPCancelConnection set correct length

The RemoteNameLength passed in the IOCTL_AFS_CANCEL_CONNECTION call
must not include the trailing NUL.  NPGetConnection() returns the
size of the buffer used which does include the trailing NUL.

Change-Id: Ic5eae51aade91db4a799bea83d898af6fbc37504
Reviewed-on: http://gerrit.openafs.org/5806
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>