nfsd4: disallow SEEK with special stateids
nfsd4: disallow SEEK with special stateids

If the client uses a special stateid then we'll pass a NULL file to
vfs_llseek.

Fixes: 24bab491220f " NFSD: Implement SEEK"
Cc: Anna Schumaker <5381043123508d4eed62c465c7c46f2f193a2767@Netapp.com>
Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org
Reported-by: Christoph Hellwig <923f7720577207a44b32e59bbfbea59d27f1ae8e@infradead.org>
Signed-off-by: J. Bruce Fields <51738506c1b2ccb0761f23bdc612c93babf738ea@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs