Undefine MBEDTLS_MPI_MAX_SIZE

Undefine `MBEDTLS_MPI_MAX_SIZE` in case it is already defined
in the configuration file.

Author: Ron Eldor

tls-client/mbedtls_entropy_config.h

@@ -33,6 +33,9 @@
  *  Set this value higher to enable handling larger keys, but be aware that this
  *  will increase the stack usage.
  */
+#if defined(MBEDTLS_MPI_MAX_SIZE)
+#undef MBEDTLS_MPI_MAX_SIZE
+#endif
 #define MBEDTLS_MPI_MAX_SIZE        256
 
 #define MBEDTLS_MPI_WINDOW_SIZE     1