nfs: set file size in namespace on stable_how is FILE_SYNC4

In some workloads, nfs client may request file size before mover
is slosed and file size is set. Nevertheless, prior such requests client
must commit written data by sending an explicit COMMIT operation
or WRITE with FILE_SYNC flag.

This change covers both cases. To match pnfsid's to mover we keep
a dedicated mapping with an assumption, that only single mover can
perform write operation.

2.11 is requested as we see the need for a sync in production system at desy.

Acked-by: Gerd Behrmann
Target: master, 2.11
Require-book: no
Require-notes: yes
(cherry picked from commit 3dca7ee2823a8157214ca351aa2013822c909c85)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
nfs: return correct verifier on WRITE and COMMIT

Acked-by: Paul Millar
Acked-by: Gerd Behrmann
Target: master
Require-book: no
Require-notes: no
(cherry picked from commit 952316ff36f15b7f4dec962ad279994dcd97bacd)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Merge pull request #1150 from kofemann/nfs-commit-2.11

nfs commit and write verifier fixes