Make DTLSv1_listen a first class function and change its type

The DTLSv1_listen function exposed details of the underlying BIO
abstraction and did not properly allow for IPv6. This commit changes the
"peer" argument to be a BIO_ADDR and makes it a first class function
(rather than a ctrl) to ensure proper type checking.

Reviewed-by: Richard Levitte <levitte@openssl.org>

apps/s_server.c

@@ -2496,7 +2496,7 @@ static int init_ssl_connection(SSL *con)
             BIO_printf(bio_err, "ERROR - memory\n");
             return 0;
         }
-        i = DTLSv1_listen(con, &client);
+        i = DTLSv1_listen(con, client);
         if (i > 0) {
             BIO *wbio;
             int fd = -1;