NFSD add vfs_fsync after async copy is done

NFSD add vfs_fsync after async copy is done

Currently, the server does all copies as NFS_UNSTABLE. For synchronous
copies linux client will append a COMMIT to the COPY compound but for
async copies it does not (because COMMIT needs to be done after all
bytes are copied and not as a reply to the COPY operation).

However, in order to save the client doing a COMMIT as a separate
rpc, the server can reply back with NFS_FILE_SYNC copy. This patch
proposed to add vfs_fsync() call at the end of the async copy.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>