http2: validate settings input

The settings input was not marked as optional in our documentation
but we did not throw an error in those cases. The API does not seem
to be useful without the correct input, so I went for throwing an
error in such cases instead of updating the documentation.

lib/internal/http2/core.js

@@ -789,7 +789,11 @@ function pingCallback(cb) {
 // 6. enablePush must be a boolean
 // All settings are optional and may be left undefined
 function validateSettings(settings) {
-  if (settings === undefined) return;
+  if (settings === undefined) {
+    const err = new ERR_INVALID_ARG_TYPE('settings', 'object', settings);
+    Error.captureStackTrace(err, 'validateSettings');
+    throw err;
+  }
   assertWithinRange('headerTableSize',
                     settings.headerTableSize,
                     0, kMaxInt);

test/parallel/test-http2-getpackedsettings.js

@@ -88,8 +88,10 @@ http2.getPackedSettings({ enablePush: false });
 
 // Check for not passing settings.
 {
-  const packed = http2.getPackedSettings();
-  assert.strictEqual(packed.length, 0);
+  assert.throws(
+    () => http2.getPackedSettings(),
+    { code: 'ERR_INVALID_ARG_TYPE' }
+  );
 }
 
 {