asio: option to use wolfSSL as TLS stack for ASIO

Plus other minor update, make openssl aware of current modes (SSL_set_mode)
Update coding style in examples and tests, including copyright notices


* Original commit: espressif/esp-idf@1c8171c3e8

components/asio/port/include/openssl/dh.h

@@ -0,0 +1,23 @@
+// Copyright 2020 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef _ESP_ASIO_OPENSSL_DH_STUB_H
+#define _ESP_ASIO_OPENSSL_DH_STUB_H
+// Dummy header needed for ASIO compilation with esp-openssl
+
+#if defined(ASIO_USE_WOLFSSL)
+#include_next "openssl/dh.h"
+#endif // ASIO_USE_WOLFSSL
+
+#endif // _ESP_ASIO_OPENSSL_DH_STUB_H