nfs4: fix orphan proxy movers

Check client state before starting a proxy mover.
This prevents orphan movers when client recovery failed
or stateid provided by client is not valid.

Acked-by: Gerd Behrmann
Target: master, 2.7
Require-book: no
Require-notes: no
(cherry picked from commit b9d945f9e1dfb47bf501870cc91f1334b33fb6dc)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #387 from kofemann/fix-nfs-movers

nfs4: fix orphan proxy movers