NFS: Pass a stateid to test_stateid() and free_stateid()

This takes the guesswork out of what stateid to use.  The caller is
expected to figure this out and pass in the correct one.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>