Use btcd pver instead of wire pver in RPC encoding.

Along the same lines as the previous commit, the RPCs that return
serialized data structures should use the max protocol version btcd
supports as opposed to the maximum protocol version etcwire supports.

rpcserver.go

@@ -537,7 +537,7 @@ func handleAddNode(s *rpcServer, cmd btcjson.Cmd) (interface{}, error) {
 // latest protocol version and returns a hex-encoded string of the result.
 func messageToHex(msg btcwire.Message) (string, error) {
 	var buf bytes.Buffer
-	err := msg.BtcEncode(&buf, btcwire.ProtocolVersion)
+	err := msg.BtcEncode(&buf, maxProtocolVersion)
 	if err != nil {
 		return "", btcjson.Error{
 			Code:    btcjson.ErrInternal.Code,