from ecdh.c:282
static int ecdh_make_params_internal( mbedtls_ecdh_context_mbed *ctx,
size_t *olen,
int point_format,
unsigned char *buf,
size_t blen,
int (*f_rng)(void *,
unsigned char *,
size_t),
void *p_rng,
int restart_enabled );