Adds ENR "eth2" field and Fork logic to networking (#953)

* Merge #913

* Correct release tests

* Completed release test corrections

* Initial work on upgrading discovery

* Updates discovery to latest version

* Update ENR initialisation logic

* Remove debug statements

* Shifts timing units to slots

* Initial work

* Add initial fork versioning and EnrForkId

* Correct linking for EnrForkId

* Adds eth2 field to local ENR

* Initial work to eth2 field integration

* Integrate eth2 field into discovery

* temp commit

* Add a timer to adjust fork versions during a hard fork for the ENR

beacon_node/src/config.rs

@@ -187,6 +187,19 @@ pub fn get_configs<E: EthSpec>(
         client_config.network.secret_key_hex = Some(p2p_priv_key.to_string());
     }
 
+    /*
+     * Chain specification
+     */
+    if let Some(disabled_forks_str) = cli_args.value_of("disabled-forks") {
+        client_config.disabled_forks = disabled_forks_str
+            .split(',')
+            .map(|fork_name| {
+                fork_name
+                    .parse()
+                    .map_err(|_| format!("Invalid fork name: {}", fork_name))
+            })
+            .collect::<Result<Vec<String>>>()?;
+    }
     /*
      * Http server
      */