afsmonitor: Allow CBSTATS collection to work

The switch which selects the collection number was missing a
'break', so selecting the CBSTATS collection would always fall
through to the default, error, case.

Caught by clang-analyzer

Reviewed-on: http://gerrit.openafs.org/9235
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 75ef02d9dfb43079f111ea22ae351cf0eec13fab)

Change-Id: I45bd1152385bdb05d1d027905b52592b1bc0869f
Reviewed-on: http://gerrit.openafs.org/10749
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>