nfsd4: convert 4.1 replay encoding

Limits on maxresp_sz mean that we only ever need to replay rpc's that
are contained entirely in the head.

The one exception is very small zero-copy reads.  That's an odd corner
case as clients wouldn't normally ask those to be cached.

in any case, this seems a little more robust.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4xdr.c

@@ -3659,7 +3659,7 @@ nfsd4_encode_sequence(struct nfsd4_compoundres *resp, __be32 nfserr,
 	WRITE32(seq->maxslots - 1); /* sr_target_highest_slotid */
 	WRITE32(seq->status_flags);
 
-	resp->cstate.datap = p; /* DRC cache data pointer */
+	resp->cstate.data_offset = xdr->buf->len; /* DRC cache data pointer */
 	return 0;
 }