extmod/mbedtls: Implement recommended DTLS features, make optional.

- DTLS spec recommends HelloVerify and Anti Replay protection be enabled,
  and these are enabled in the default mbedTLS config. Implement them here.

- To help compensate for the possible increase in code size, add a
  MICROPY_PY_SSL_DTLS build config macro that's enabled for EXTRA and
  above by default.

This allows bare metal mbedTLS ports to use DTLS with HelloVerify support.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

extmod/mbedtls/mbedtls_config_common.h

@@ -26,6 +26,8 @@
 #ifndef MICROPY_INCLUDED_MBEDTLS_CONFIG_COMMON_H
 #define MICROPY_INCLUDED_MBEDTLS_CONFIG_COMMON_H
 
+#include "py/mpconfig.h"
+
 // If you want to debug MBEDTLS uncomment the following and
 // pass "3" to mbedtls_debug_set_threshold in socket_new.
 // #define MBEDTLS_DEBUG_C
@@ -89,12 +91,18 @@
 #define MBEDTLS_SHA384_C
 #define MBEDTLS_SHA512_C
 #define MBEDTLS_SSL_CLI_C
-#define MBEDTLS_SSL_PROTO_DTLS
 #define MBEDTLS_SSL_SRV_C
 #define MBEDTLS_SSL_TLS_C
 #define MBEDTLS_X509_CRT_PARSE_C
 #define MBEDTLS_X509_USE_C
 
+#if MICROPY_PY_SSL_DTLS
+#define MBEDTLS_SSL_PROTO_DTLS
+#define MBEDTLS_SSL_DTLS_ANTI_REPLAY
+#define MBEDTLS_SSL_DTLS_HELLO_VERIFY
+#define MBEDTLS_SSL_COOKIE_C
+#endif
+
 // A port may enable this option to select additional bare-metal configuration.
 #if MICROPY_MBEDTLS_CONFIG_BARE_METAL