NFSD: Save location of NFSv4 COMPOUND status

Refactor: Currently nfs4svc_encode_compoundres() relies on the NFS
dispatcher to pass in the buffer location of the COMPOUND status.
Instead, save that buffer location in struct nfsd4_compoundres.

The compound tag follows immediately after.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 5895bbe..a36261f 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -2461,11 +2461,11 @@ nfsd4_proc_compound(struct svc_rqst *rqstp)
 	__be32		status;
 
 	resp->xdr = &rqstp->rq_res_stream;
+	resp->statusp = resp->xdr->p;
 
 	/* reserve space for: NFS status code */
 	xdr_reserve_space(resp->xdr, XDR_UNIT);
 
-	resp->tagp = resp->xdr->p;
 	/* reserve space for: taglen, tag, and opcnt */
 	xdr_reserve_space(resp->xdr, XDR_UNIT * 2 + args->taglen);
 	resp->taglen = args->taglen;