nfsd4: Remove check for a 32-bit cookie in nfsd4_readdir()

Fan Yong <yong.fan@whamcloud.com> noticed setting
FMODE_32bithash wouldn't work with nfsd v4, as
nfsd4_readdir() checks for 32 bit cookies. However, according to RFC 3530
cookies have a 64 bit type and cookies are also defined as u64 in
'struct nfsd4_readdir'. So remove the test for >32-bit values.

Cc: stable@kernel.org
Signed-off-by: Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>