nfs4: clean failed request from pending queue

if door have failed to start a mover, then we have to
clean pending message queue to avoid dead records. A
new entry will be created on client retry.

Acked-by: Gerd Behrmann
Target: master, 2.7, 2.8
Require-book: no
Require-notes: no
(cherry picked from commit 9f78b39ca1aac8418e9adea9c1ab219316178ce8)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #437 from kofemann/clean-dead-request-2.7

nfs4: clean failed request from pending queue