http2: remove side effects from validateSettings

The function did not only validate the input so far but it also made
a copy of the input object and returned that copy to the callee
function. That copy was not necessary for all call sites and it was
not obvious that the function did not only validate the input but
that it also returned a copy of it. This makes sure the function does
nothing more than validation and copying is happening in the callee
function when required.

lib/internal/http2/core.js

@@ -789,7 +789,7 @@ function pingCallback(cb) {
 // 6. enablePush must be a boolean
 // All settings are optional and may be left undefined
 function validateSettings(settings) {
-  settings = { ...settings };
+  if (settings === undefined) return;
   assertWithinRange('headerTableSize',
                     settings.headerTableSize,
                     0, kMaxInt);
@@ -813,7 +813,6 @@ function validateSettings(settings) {
     Error.captureStackTrace(err, 'validateSettings');
     throw err;
   }
-  return settings;
 }
 
 // Creates the internal binding.Http2Session handle for an Http2Session
@@ -1152,15 +1151,15 @@ class Http2Session extends EventEmitter {
     if (this.destroyed)
       throw new ERR_HTTP2_INVALID_SESSION();
     assertIsObject(settings, 'settings');
-    settings = validateSettings(settings);
+    validateSettings(settings);
 
     if (callback && typeof callback !== 'function')
       throw new ERR_INVALID_CALLBACK();
     debug(`Http2Session ${sessionName(this[kType])}: sending settings`);
 
     this[kState].pendingAck++;
 
-    const settingsFn = submitSettings.bind(this, settings, callback);
+    const settingsFn = submitSettings.bind(this, { ...settings }, callback);
     if (this.connecting) {
       this.once('connect', settingsFn);
       return;
@@ -2830,7 +2829,8 @@ function createServer(options, handler) {
 // HTTP2-Settings header frame.
 function getPackedSettings(settings) {
   assertIsObject(settings, 'settings');
-  updateSettingsBuffer(validateSettings(settings));
+  validateSettings(settings);
+  updateSettingsBuffer({ ...settings });
   return binding.packSettings();
 }