tls: use validateFunction for options.checkServerIdentity

If user uses invalid type for `options.checkServerIdentity`
in tls.connect(), it's not internal issue of Node.js. So
validateFunction() is more proper than assert().

Fixes: nodejs#49839
PR-URL: nodejs#49896
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

lib/_tls_wrap.js

@@ -1738,7 +1738,7 @@ exports.connect = function connect(...args) {
   if (!options.keepAlive)
     options.singleUse = true;
 
-  assert(typeof options.checkServerIdentity === 'function');
+  validateFunction(options.checkServerIdentity, 'options.checkServerIdentity');
   assert(typeof options.minDHSize === 'number',
          'options.minDHSize is not a number: ' + options.minDHSize);
   assert(options.minDHSize > 0,

test/parallel/test-tls-basic-validations.js

@@ -135,3 +135,12 @@ assert.throws(() => { tls.createSecureContext({ maxVersion: 'fhqwhgads' }); },
                 code: 'ERR_TLS_INVALID_PROTOCOL_VERSION',
                 name: 'TypeError'
               });
+
+for (const checkServerIdentity of [undefined, null, 1, true]) {
+  assert.throws(() => {
+    tls.connect({ checkServerIdentity });
+  }, {
+    code: 'ERR_INVALID_ARG_TYPE',
+    name: 'TypeError',
+  });
+}