nfsd: simplify stateid allocation and file handling
Don't allow stateids to clear the open file pointer until they are
being destroyed. In a later patches we'll want to rely on the fact that
we have a valid file pointer when dealing with the stateid and this
will save us from having to do a lot of NULL pointer checks before
doing so.
Also, move to allocating stateids with kzalloc and get rid of the
explicit zeroing of fields.
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: J. Bruce Fields <bfields@redhat.com>