disable Rx packet tracking

disable Rx packet tracking

minimize the impact of Rx packet tracking. in particular, do no
extra queue scans, which means the rest of the state which tracks
where a packet is now isn't of use. make it possible to re-enable.

Change-Id: I5b9ed039a0394edcea48bb46729cd2ce2f71d4b9
Reviewed-on: http://gerrit.openafs.org/2762
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>