afs: put back conn if not using in checkserver loop

afs: put back conn if not using in checkserver loop

we get a conn, check it for eligibility, and if not,
just abandon it. "oops"

(cherry picked from commit 26fc0cda94c24a1c5f0bef109bca920456c25265)

Change-Id: I8e4f762b5170f07d6abc3508e88f001ca147c3a7
Reviewed-on: http://gerrit.openafs.org/6521
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>