Further libssl size_t-ify of reading

Writing still to be done

Reviewed-by: Rich Salz <rsalz@openssl.org>
diff --git a/ssl/statem/statem_clnt.c b/ssl/statem/statem_clnt.c
index 51513d5..5704654 100644
--- a/ssl/statem/statem_clnt.c
+++ b/ssl/statem/statem_clnt.c
@@ -568,7 +568,7 @@
  * Returns the maximum allowed length for the current message that we are
  * reading. Excludes the message header.
  */
-unsigned long ossl_statem_client_max_message_size(SSL *s)
+size_t ossl_statem_client_max_message_size(SSL *s)
 {
     OSSL_STATEM *st = &s->statem;