Ignore self as a bootnode (#4110)

If a node is also a bootnode it can try to add itself to its own local routing table which will emit an error. 

The error is entirely harmless but we would prefer to avoid emitting the error. 

This PR does not attempt to add a boot node ENR if that ENR corresponds to our local peer-id/node-id.

beacon_node/lighthouse_network/src/discovery/mod.rs

@@ -197,6 +197,7 @@ impl<TSpec: EthSpec> Discovery<TSpec> {
         };
 
         let local_enr = network_globals.local_enr.read().clone();
+        let local_node_id = local_enr.node_id();
 
         info!(log, "ENR Initialised"; "enr" => local_enr.to_base64(), "seq" => local_enr.seq(), "id"=> %local_enr.node_id(),
               "ip4" => ?local_enr.ip4(), "udp4"=> ?local_enr.udp4(), "tcp4" => ?local_enr.tcp6()
@@ -217,6 +218,10 @@ impl<TSpec: EthSpec> Discovery<TSpec> {
 
         // Add bootnodes to routing table
         for bootnode_enr in config.boot_nodes_enr.clone() {
+            if bootnode_enr.node_id() == local_node_id {
+                // If we are a boot node, ignore adding it to the routing table
+                continue;
+            }
             debug!(
                 log,
                 "Adding node to routing table";