rust/template: suppress unread variable warning

Suppress the warning about an unused variable in the template
parser. As this is just a template I think this is OK, however
master should make sure this variable is used, if only to be
more self documenting.

rust/src/applayertemplate/template.rs

@@ -67,6 +67,7 @@ pub struct TemplateState {
     tx_id: u64,
     transactions: Vec<TemplateTransaction>,
     request_gap: bool,
+    #[allow(dead_code)]
     response_gap: bool,
 }