Update cookie_len for size_t

Reviewed-by: Rich Salz <rsalz@openssl.org>
diff --git a/ssl/statem/statem_clnt.c b/ssl/statem/statem_clnt.c
index 3129456..af08825 100644
--- a/ssl/statem/statem_clnt.c
+++ b/ssl/statem/statem_clnt.c
@@ -870,7 +870,7 @@
 MSG_PROCESS_RETURN dtls_process_hello_verify(SSL *s, PACKET *pkt)
 {
     int al;
-    unsigned int cookie_len;
+    size_t cookie_len;
     PACKET cookiepkt;
 
     if (!PACKET_forward(pkt, 2)