Add set outbound transform

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>

library/ssl_tls13_keys.h

@@ -638,6 +638,17 @@ int mbedtls_ssl_tls13_calculate_verify_data( mbedtls_ssl_context *ssl,
                                              size_t *actual_len,
                                              int which );
 
+/**
+ * \brief Compute TLS 1.3 handshake transform
+ *
+ * \param ssl  The SSL context to operate on. The early secrtet must have been
+ *             computed.
+ *
+ * \returns    \c 0 on success.
+ * \returns    A negative error code on failure.
+ */
+int mbedtls_ssl_tls13_set_handshake_transform( mbedtls_ssl_context *ssl );
+
 #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
 
 #endif /* MBEDTLS_SSL_TLS1_3_KEYS_H */