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>
(cherry picked from commit 4bbf0dae237e01127f4d1a4d913f00e8dad859a3)
Reviewed-on: http://gerrit.openafs.org/2796
Tested-by: Derrick Brashear <shadow@dementia.org>