Change cookie free code and some comments

Signed-off-by: XiaokangQian <xiaokang.qian@arm.com>
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 7bd3118..0c43c79 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -694,9 +694,11 @@
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS) || defined(MBEDTLS_SSL_PROTO_TLS1_3)
     unsigned char *verify_cookie;       /*!<  Cli: HelloVerifyRequest cookie
-                                              Srv: unused                    */
-    unsigned char verify_cookie_len;    /*!<  Cli: cookie length
-                                              Srv: flag for sending a cookie */
+                                         *    for dtls / tls 1.3
+                                         *    Srv: unused                    */
+    unsigned char verify_cookie_len;    /*!<  Cli: cookie length for
+                                         *    dtls / tls 1.3
+                                         *    Srv: flag for sending a cookie */
 #endif /* MBEDTLS_SSL_PROTO_DTLS || MBEDTLS_SSL_PROTO_TLS1_3 */
 
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 6f37201..82da11f 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -5689,11 +5689,11 @@
     mbedtls_pk_free( &handshake->peer_pubkey );
 #endif /* MBEDTLS_X509_CRT_PARSE_C && !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
 
-#if defined(MBEDTLS_SSL_PROTO_DTLS)
+#if defined(MBEDTLS_SSL_PROTO_DTLS) || defined(MBEDTLS_SSL_PROTO_TLS1_3)
     mbedtls_free( handshake->verify_cookie );
     mbedtls_ssl_flight_free( handshake->flight );
     mbedtls_ssl_buffering_free( ssl );
-#endif
+#endif /* MBEDTLS_SSL_PROTO_DTLS || MBEDTLS_SSL_PROTO_TLS1_3 */
 
 #if defined(MBEDTLS_ECDH_C) &&                  \
     defined(MBEDTLS_USE_PSA_CRYPTO)
diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index b8f4bce..75978a8 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -559,6 +559,7 @@
     MBEDTLS_SSL_DEBUG_BUF( 3, "cookie extension", p, cookie_len );
 
     mbedtls_free( handshake->verify_cookie );
+    handshake->verify_cookie_len = 0;
     handshake->verify_cookie = mbedtls_calloc( 1, cookie_len );
     if( handshake->verify_cookie == NULL )
     {