Fix exit debts

Exit debt computation has been broken since the commit "Add config
options for exit routing overhaul" due to confusion about mutable
references that somehow did not trigger rusts usuall warning about
unused mutated references.

This caused debts from the previous loop to not persist resulting in
client overbilling as each loop iteration they would be billed for
traffic from all previous loops.

rita_exit/src/rita_loop/mod.rs

@@ -249,7 +249,7 @@ pub async fn start_rita_exit_loop(client_and_ip_info: Arc<RwLock<ClientListAnIpA
             babel_port,
             start,
             rita_exit_cache.get_all_registered_clients(),
-            rita_exit_cache.usage_history.clone(),
+            &mut rita_exit_cache.usage_history,
         );
         info!(
             "Finished Rita billing in {}ms",
@@ -342,7 +342,7 @@ fn bill(
     babel_port: u16,
     start: Instant,
     ids: HashSet<Identity>,
-    usage_history: HashMap<WgKey, WgUsage>,
+    usage_history: &mut HashMap<WgKey, WgUsage>,
 ) {
     trace!("about to try opening babel stream");
 

rita_exit/src/traffic_watcher/mod.rs

@@ -145,7 +145,7 @@ fn debts_logging(debts: &HashMap<Identity, i128>) {
 
 /// This traffic watcher watches how much traffic each we send and receive from each client.
 pub fn watch_exit_traffic(
-    mut usage_history: HashMap<WgKey, WgUsage>,
+    usage_history: &mut HashMap<WgKey, WgUsage>,
     routes: &[Route],
     clients: Vec<Identity>,
 ) -> Result<(), Box<RitaExitError>> {
@@ -194,7 +194,7 @@ pub fn watch_exit_traffic(
     trace!("merged counters are : {:?}", counters);
 
     // creates new usage entires does not actualy update the values
-    prepare_usage_history(&counters, &mut usage_history);
+    prepare_usage_history(&counters, usage_history);
 
     counters_logging(&counters, &usage_history, our_price as u32);