Stick to 'ephemeral' instead of ECDHE for TLS 1.3 key exchanges

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 5d0cf3e..70dc501 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -2631,7 +2631,7 @@
  *        mbedtls_ssl_conf_psk_cb() or mbedtls_ssl_conf_psk_opaque()
  *        to configure the PSKs to be used.
  *
- * \note  If an ECDHE-based key exchange mode shall be supported,
+ * \note  If a pure-ephemeral key exchange mode shall be supported,
  *        server-side applications must also provide a certificate via
  *        mbedtls_ssl_conf_own_cert().
  *