afs: Panic on afs_conn refcount imbalance

afs: Panic on afs_conn refcount imbalance

An undercounted afs_conn can easily cause a panic and/or memory
corruption later on, since we put an rx_connection reference with each
afs_conn reference. Panic as soon as we detect this, as this indicates
a serious bug.

Reviewed-on: http://gerrit.openafs.org/6413
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 8a574ba16a80fc2b8b703ddcfc99486b977e6071)

Change-Id: Ibd60dafdf1a800349b73754dae18666fa0edd300
Reviewed-on: http://gerrit.openafs.org/6642
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>