[Java] Stop processing net before we stop the background processor

See https://github.com/lightningdevkit/rust-lightning/issues/1237A

Fixes #77.

Author: TheBlueMatt

src/main/java/org/ldk/batteries/ChannelManagerConstructor.java

@@ -207,7 +207,7 @@ public void chain_sync_completed(EventHandler event_handler, @Nullable MultiThre
      * Interrupt the background thread, stopping the background handling of events.
      */
     public void interrupt() {
-        this.background_processor.stop();
         this.nio_peer_handler.interrupt();
+        this.background_processor.stop();
     }
 }