nfsd: restrict rd_maxcount to svc_max_payload in nfsd_encode_readdir

nfsd: restrict rd_maxcount to svc_max_payload in nfsd_encode_readdir

BugLink: http://bugs.launchpad.net/bugs/1807469
commit 9c2ece6ef67e9d376f32823086169b489c422ed0 upstream.

nfsd4_readdir_rsize restricts rd_maxcount to svc_max_payload when
estimating the size of the readdir reply, but nfsd_encode_readdir
restricts it to INT_MAX when encoding the reply.  This can result in log
messages like "kernel: RPC request reserved 32896 but used 1049444".

Restrict rd_dircount similarly (no reason it should be larger than
svc_max_payload).

Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>