test: pummel/test-net-throttle adhere to streams

bufferSize is now a getter that shows all that has not been
acknowledged by the os, as well as in the buffer state. The test is
only looking to verify the js verified state.

test/pummel/test-net-throttle.js

@@ -43,8 +43,8 @@ var server = net.createServer(function(connection) {
   connection.write(body.slice(0, part_N));
   connection.write(body.slice(part_N, 2 * part_N));
   assert.equal(false, connection.write(body.slice(2 * part_N, N)));
-  console.log('bufferSize: ' + connection.bufferSize);
-  assert.ok(0 <= connection.bufferSize && connection.bufferSize <= N);
+  console.log('bufferSize: ' + connection.bufferSize, 'expecting', N);
+  assert.ok(0 <= connection.bufferSize && connection._writableState.length <= N);
   connection.end();
 });