NFS: Make nfs_fsync methods consistent

Clean up: Report the same debugging info, count function calls the same,
and use similar function naming in nfs_fsync_dir() and nfs_fsync().

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>