IDONTWANT message optimisation to cutoff for smaller messages (#6456)

* idontwant message opitmising

* requested changes and linter appeasing

* added the config cli flag

* Merge branch 'unstable' into fix/idontwant-optimise

* cli docs generated

* const declaration

* Hide extra technical cli flag

* passing ci

* Merge branch 'unstable' into fix/idontwant-optimise

beacon_node/lighthouse_network/gossipsub/src/behaviour.rs

@@ -1812,9 +1812,6 @@ where
         // Calculate the message id on the transformed data.
         let msg_id = self.config.message_id(&message);
 
-        // Broadcast IDONTWANT messages.
-        self.send_idontwant(&raw_message, &msg_id, propagation_source);
-
         // Check the validity of the message
         // Peers get penalized if this message is invalid. We don't add it to the duplicate cache
         // and instead continually penalize peers that repeatedly send this message.
@@ -1830,6 +1827,12 @@ where
             self.mcache.observe_duplicate(&msg_id, propagation_source);
             return;
         }
+
+        // Broadcast IDONTWANT messages
+        if raw_message.raw_protobuf_len() > self.config.idontwant_message_size_threshold() {
+            self.send_idontwant(&raw_message, &msg_id, propagation_source);
+        }
+
         tracing::debug!(
             message=%msg_id,
             "Put message in duplicate_cache and resolve promises"