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)