lnrpc+rpcperms+lntest: add unique MW message ID

This commit adds a new unique intercept message ID that is different for
each message sent to an RPC middleware. This will allow us to re-purpose
the existing request ID field into its original intention, which was to
have a unique ID for a full gRPC request/response pair or gRPC stream as
a whole.

lntest/itest/lnd_rpc_middleware_interceptor_test.go

@@ -537,7 +537,7 @@ func (h *middlewareHarness) interceptUnary(methodURI string,
 	assertInterceptedType(h.t, expectedRequest, req)
 
 	// We need to accept the request.
-	h.sendAccept(reqIntercept.RequestId, nil)
+	h.sendAccept(reqIntercept.MsgId, nil)
 
 	// Now read the intercept message for the response.
 	respIntercept, err := h.stream.Recv()
@@ -546,7 +546,7 @@ func (h *middlewareHarness) interceptUnary(methodURI string,
 	require.NotNil(h.t, res)
 
 	// We need to accept the response as well.
-	h.sendAccept(respIntercept.RequestId, responseReplacement)
+	h.sendAccept(respIntercept.MsgId, responseReplacement)
 
 	h.responsesChan <- res
 }
@@ -571,7 +571,7 @@ func (h *middlewareHarness) interceptStream(methodURI string,
 	require.Equal(h.t, methodURI, auth.MethodFullUri)
 
 	// We need to accept the auth.
-	h.sendAccept(authIntercept.RequestId, nil)
+	h.sendAccept(authIntercept.MsgId, nil)
 
 	// Read intercept message and make sure it's for an RPC request.
 	reqIntercept, err := h.stream.Recv()
@@ -585,7 +585,7 @@ func (h *middlewareHarness) interceptStream(methodURI string,
 	assertInterceptedType(h.t, expectedRequest, req)
 
 	// We need to accept the request.
-	h.sendAccept(reqIntercept.RequestId, nil)
+	h.sendAccept(reqIntercept.MsgId, nil)
 
 	// Now read the intercept message for the response.
 	respIntercept, err := h.stream.Recv()
@@ -594,13 +594,13 @@ func (h *middlewareHarness) interceptStream(methodURI string,
 	require.NotNil(h.t, res)
 
 	// We need to accept the response as well.
-	h.sendAccept(respIntercept.RequestId, responseReplacement)
+	h.sendAccept(respIntercept.MsgId, responseReplacement)
 
 	h.responsesChan <- res
 }
 
 // sendAccept sends an accept feedback to the RPC server.
-func (h *middlewareHarness) sendAccept(requestID uint64,
+func (h *middlewareHarness) sendAccept(msgID uint64,
 	responseReplacement proto.Message) {
 
 	var replacementBytes []byte
@@ -617,7 +617,7 @@ func (h *middlewareHarness) sendAccept(requestID uint64,
 				ReplacementSerialized: replacementBytes,
 			},
 		},
-		RequestId: requestID,
+		RefMsgId: msgID,
 	})
 	require.NoError(h.t, err)
 }