tls13: Use a flag not a counter for CCS and HRR handling

Reconcile with 5fbd27055d15c8ac234a229389ff4e31977487a0 on another branch

Signed-off-by: Gilles Peskine <gilles.peskine@arm.com>
diff --git a/library/ssl_client.c b/library/ssl_client.c
index 371c06c..345e608 100644
--- a/library/ssl_client.c
+++ b/library/ssl_client.c
@@ -793,7 +793,7 @@
 #endif
     {
 #if defined(MBEDTLS_SSL_PROTO_TLS1_3)
-        if (ssl->handshake->hello_retry_request_count == 0)
+        if (!ssl->handshake->hello_retry_request_flag)
 #endif
         {
             ret = ssl_generate_random(ssl);