[crypto] Do not use otPlatCAlloc and otPlatFree directly in mbedtls

This commit changes the default configuration of heap memory in mbedtls
when OPENTHREAD_CONFIG_HEAP_EXTERNAL_ENABLE is enabled.

This is necessary to pass the unit tests which keep track of heap memory
with crypto backend that allocates memory during the test.

Signed-off-by: Łukasz Duda <lukasz.duda@nordicsemi.no>

Author: LuDuda

src/core/crypto/mbedtls.cpp

@@ -57,9 +57,9 @@ MbedTls::MbedTls(void)
     // mbedTLS's debug level is almost the same as OpenThread's
     mbedtls_debug_set_threshold(OPENTHREAD_CONFIG_LOG_LEVEL);
 #endif
-#if OPENTHREAD_CONFIG_ENABLE_BUILTIN_MBEDTLS_MANAGEMENT
+#if OPENTHREAD_CONFIG_ENABLE_BUILTIN_MBEDTLS_MANAGEMENT && !OPENTHREAD_CONFIG_HEAP_EXTERNAL_ENABLE
     mbedtls_platform_set_calloc_free(Heap::CAlloc, Heap::Free);
-#endif // OPENTHREAD_CONFIG_ENABLE_BUILTIN_MBEDTLS_MANAGEMENT
+#endif // OPENTHREAD_CONFIG_ENABLE_BUILTIN_MBEDTLS_MANAGEMENT && !OPENTHREAD_CONFIG_HEAP_EXTERNAL_ENABLE
 }
 
 Error MbedTls::MapError(int aMbedTlsError)

third_party/mbedtls/mbedtls-config.h

@@ -134,8 +134,8 @@
 #define MBEDTLS_ENTROPY_MAX_SOURCES        1 /**< Maximum number of sources supported */
 
 #if OPENTHREAD_CONFIG_HEAP_EXTERNAL_ENABLE
-#define MBEDTLS_PLATFORM_STD_CALLOC      otPlatCAlloc /**< Default allocator to use, can be undefined */
-#define MBEDTLS_PLATFORM_STD_FREE        otPlatFree /**< Default free to use, can be undefined */
+#define MBEDTLS_PLATFORM_STD_CALLOC      calloc /**< Default allocator to use, can be undefined */
+#define MBEDTLS_PLATFORM_STD_FREE        free /**< Default free to use, can be undefined */
 #else
 #define MBEDTLS_MEMORY_BUFFER_ALLOC_C
 #endif