Revert "Remove unused TLS, NET, and X.509 files"

This reverts commit a4308b29a42a00fcbffa7d6d041946feeddc0ce9.
diff --git a/include/mbedtls/net.h b/include/mbedtls/net.h
new file mode 100644
index 0000000..8cead58
--- /dev/null
+++ b/include/mbedtls/net.h
@@ -0,0 +1,37 @@
+/**
+ * \file net.h
+ *
+ * \brief Deprecated header file that includes net_sockets.h
+ *
+ * \deprecated Superseded by mbedtls/net_sockets.h
+ */
+/*
+ *  Copyright (C) 2006-2016, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  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.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#if !defined(MBEDTLS_DEPRECATED_REMOVED)
+#include "net_sockets.h"
+#if defined(MBEDTLS_DEPRECATED_WARNING)
+#warning "Deprecated header file: Superseded by mbedtls/net_sockets.h"
+#endif /* MBEDTLS_DEPRECATED_WARNING */
+#endif /* !MBEDTLS_DEPRECATED_REMOVED */