Change code based on comments

Move set_state function into client
Add back export_key callback function in generate
application keys

Signed-off-by: XiaokangQian <xiaokang.qian@arm.com>
diff --git a/library/ssl_tls13_keys.c b/library/ssl_tls13_keys.c
index 34d8a19..b97a70f 100644
--- a/library/ssl_tls13_keys.c
+++ b/library/ssl_tls13_keys.c
@@ -1189,6 +1189,26 @@
                            app_secrets->server_application_traffic_secret_N,
                            md_size );
 
+    /*
+     * Export client/server application traffic secret 0
+     */
+    if( ssl->f_export_keys != NULL )
+    {
+        ssl->f_export_keys( ssl->p_export_keys,
+                MBEDTLS_SSL_KEY_EXPORT_TLS13_CLIENT_APPLICATION_TRAFFIC_SECRET,
+                app_secrets->client_application_traffic_secret_N, md_size,
+                ssl->handshake->randbytes + 32,
+                ssl->handshake->randbytes,
+                MBEDTLS_SSL_TLS_PRF_NONE /* TODO: FIX! */ );
+
+        ssl->f_export_keys( ssl->p_export_keys,
+                MBEDTLS_SSL_KEY_EXPORT_TLS13_SERVER_APPLICATION_TRAFFIC_SECRET,
+                app_secrets->server_application_traffic_secret_N, md_size,
+                ssl->handshake->randbytes + 32,
+                ssl->handshake->randbytes,
+                MBEDTLS_SSL_TLS_PRF_NONE /* TODO: FIX! */ );
+    }
+
     MBEDTLS_SSL_DEBUG_BUF( 4, "client application_write_key:",
                               traffic_keys->client_write_key, keylen );
     MBEDTLS_SSL_DEBUG_BUF( 4, "server application write key",