NFSD: Encoder and decoder functions are always present

nfsd_dispatch() is a hot path. Let's optimize the XDR method calls
for the by-far common case, which is that the XDR methods are indeed
present.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
index aae514d4..e540fd1 100644
--- a/fs/nfsd/nfs3xdr.c
+++ b/fs/nfsd/nfs3xdr.c
@@ -305,6 +305,12 @@ void fill_post_wcc(struct svc_fh *fhp)
  * XDR decode functions
  */
 int
+nfs3svc_decode_voidarg(struct svc_rqst *rqstp, __be32 *p)
+{
+	return 1;
+}
+
+int
 nfs3svc_decode_fhandle(struct svc_rqst *rqstp, __be32 *p)
 {
 	struct nfsd_fhandle *args = rqstp->rq_argp;