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/src/service/mod.rs

@@ -237,6 +237,7 @@ impl<E: EthSpec> Network<E> {
             gossipsub_config_params,
             ctx.chain_spec.seconds_per_slot,
             E::slots_per_epoch(),
+            config.idontwant_message_size_threshold,
         );
 
         let score_settings = PeerScoreSettings::new(&ctx.chain_spec, gs_config.mesh_n());