nfs-proxy: fix logging CDC

Acked-by: Gerd Behrmann
Target: master, 2.8, 2.7
Require-book: no
Require-notes: no
(cherry picked from commit 6e7943fe960f165ab9474188c59c79bc6f61c64a)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #434 from kofemann/cdc-2.8

nfs-proxy: fix logging CDC