Refactor cookie members of handshake struct

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_tls12_client.c b/library/ssl_tls12_client.c
index 5def8b6..dd55456 100644
--- a/library/ssl_tls12_client.c
+++ b/library/ssl_tls12_client.c
@@ -1200,7 +1200,7 @@
     }
 
     memcpy( ssl->handshake->cookie, p, cookie_len );
-    ssl->handshake->verify_cookie_len = cookie_len;
+    ssl->handshake->cookie_len = cookie_len;
 
     /* Start over at ClientHello */
     ssl->state = MBEDTLS_SSL_CLIENT_HELLO;
@@ -1284,7 +1284,7 @@
             /* We made it through the verification process */
             mbedtls_free( ssl->handshake->cookie );
             ssl->handshake->cookie = NULL;
-            ssl->handshake->verify_cookie_len = 0;
+            ssl->handshake->cookie_len = 0;
         }
     }
 #endif /* MBEDTLS_SSL_PROTO_DTLS */