Externals: Update mbedtls to 2.16.1

On a few of our buildbot instances, we get warnings about the usage of
deprecated functions. We should correct these, especially if we're
delegating to system versions of the libraries if they're available.
However, in order to do that, we need to update our library variant from
2.1.1 so that the non-deprecated alternatives are actually available.

Externals/mbedtls/include/mbedtls/net_sockets.h

@@ -1,8 +1,25 @@
 /**
  * \file net_sockets.h
  *
- * \brief Network communication functions
+ * \brief   Network sockets abstraction layer to integrate Mbed TLS into a
+ *          BSD-style sockets API.
  *
+ *          The network sockets module provides an example integration of the
+ *          Mbed TLS library into a BSD sockets implementation. The module is
+ *          intended to be an example of how Mbed TLS can be integrated into a
+ *          networking stack, as well as to be Mbed TLS's network integration
+ *          for its supported platforms.
+ *
+ *          The module is intended only to be used with the Mbed TLS library and
+ *          is not intended to be used by third party application software
+ *          directly.
+ *
+ *          The supported platforms are as follows:
+ *              * Microsoft Windows and Windows CE
+ *              * POSIX/Unix platforms including Linux, OS X
+ *
+ */
+/*
  *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
  *  SPDX-License-Identifier: Apache-2.0
  *
@@ -45,12 +62,17 @@
 #define MBEDTLS_ERR_NET_UNKNOWN_HOST                      -0x0052  /**< Failed to get an IP address for the given hostname. */
 #define MBEDTLS_ERR_NET_BUFFER_TOO_SMALL                  -0x0043  /**< Buffer is too small to hold the data. */
 #define MBEDTLS_ERR_NET_INVALID_CONTEXT                   -0x0045  /**< The context is invalid, eg because it was free()ed. */
+#define MBEDTLS_ERR_NET_POLL_FAILED                       -0x0047  /**< Polling the net context failed. */
+#define MBEDTLS_ERR_NET_BAD_INPUT_DATA                    -0x0049  /**< Input invalid. */
 
 #define MBEDTLS_NET_LISTEN_BACKLOG         10 /**< The backlog that listen() should use. */
 
 #define MBEDTLS_NET_PROTO_TCP 0 /**< The TCP transport protocol */
 #define MBEDTLS_NET_PROTO_UDP 1 /**< The UDP transport protocol */
 
+#define MBEDTLS_NET_POLL_READ  1 /**< Used in \c mbedtls_net_poll to check for pending data  */
+#define MBEDTLS_NET_POLL_WRITE 2 /**< Used in \c mbedtls_net_poll to check if write possible */
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -62,7 +84,7 @@ extern "C" {
  * (eg two file descriptors for combined IPv4 + IPv6 support, or additional
  * structures for hand-made UDP demultiplexing).
  */
-typedef struct
+typedef struct mbedtls_net_context
 {
     int fd;             /**< The underlying file descriptor                 */
 }
@@ -117,9 +139,10 @@ int mbedtls_net_bind( mbedtls_net_context *ctx, const char *bind_ip, const char
  *
  * \param bind_ctx  Relevant socket
  * \param client_ctx Will contain the connected client socket
- * \param client_ip Will contain the client IP address
+ * \param client_ip Will contain the client IP address, can be NULL
  * \param buf_size  Size of the client_ip buffer
- * \param ip_len    Will receive the size of the client IP written
+ * \param ip_len    Will receive the size of the client IP written,
+ *                  can be NULL if client_ip is null
  *
  * \return          0 if successful, or
  *                  MBEDTLS_ERR_NET_ACCEPT_FAILED, or
@@ -131,6 +154,29 @@ int mbedtls_net_accept( mbedtls_net_context *bind_ctx,
                         mbedtls_net_context *client_ctx,
                         void *client_ip, size_t buf_size, size_t *ip_len );
 
+/**
+ * \brief          Check and wait for the context to be ready for read/write
+ *
+ * \param ctx      Socket to check
+ * \param rw       Bitflag composed of MBEDTLS_NET_POLL_READ and
+ *                 MBEDTLS_NET_POLL_WRITE specifying the events
+ *                 to wait for:
+ *                 - If MBEDTLS_NET_POLL_READ is set, the function
+ *                   will return as soon as the net context is available
+ *                   for reading.
+ *                 - If MBEDTLS_NET_POLL_WRITE is set, the function
+ *                   will return as soon as the net context is available
+ *                   for writing.
+ * \param timeout  Maximal amount of time to wait before returning,
+ *                 in milliseconds. If \c timeout is zero, the
+ *                 function returns immediately. If \c timeout is
+ *                 -1u, the function blocks potentially indefinitely.
+ *
+ * \return         Bitmask composed of MBEDTLS_NET_POLL_READ/WRITE
+ *                 on success or timeout, or a negative return code otherwise.
+ */
+int mbedtls_net_poll( mbedtls_net_context *ctx, uint32_t rw, uint32_t timeout );
+
 /**
  * \brief          Set the socket blocking
  *