Increase network limits (#2796)

Fix max packet sizes

Fix max_payload_size function

Add merge block test

Fix max size calculation; fix up test

Clear comments

Add a payload_size_function

Use safe arith for payload calculation

Return an error if block too big in block production

Separate test to check if block is over limit

beacon_node/lighthouse_network/src/lib.rs

@@ -16,6 +16,8 @@ pub mod rpc;
 mod service;
 pub mod types;
 
+pub use config::GOSSIP_MAX_SIZE;
+
 use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
 use std::str::FromStr;