libafs: put connection always in getcapabilities helper

libafs: put connection always in getcapabilities helper

if we get a connection, we need to always put it back. here we exited
with error before doing so. 1.6 only fix

Change-Id: I67abec863c1d60d557277468a681847263d783a1
Reviewed-on: http://gerrit.openafs.org/7570
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementix.org>