Unban peers at the swarm level when purged (#2855)

## Issue Addressed
#2840

beacon_node/lighthouse_network/src/peer_manager/mod.rs

@@ -638,7 +638,7 @@ impl<TSpec: EthSpec> PeerManager<TSpec> {
     ///
     /// This is also called when dialing a peer fails.
     fn inject_disconnect(&mut self, peer_id: &PeerId) {
-        let ban_operation = self
+        let (ban_operation, purged_peers) = self
             .network_globals
             .peers
             .write()
@@ -653,6 +653,11 @@ impl<TSpec: EthSpec> PeerManager<TSpec> {
         self.inbound_ping_peers.remove(peer_id);
         self.outbound_ping_peers.remove(peer_id);
         self.status_peers.remove(peer_id);
+        self.events.extend(
+            purged_peers
+                .into_iter()
+                .map(|(peer_id, unbanned_ips)| PeerManagerEvent::UnBanned(peer_id, unbanned_ips)),
+        );
     }
 
     /// Registers a peer as connected. The `ingoing` parameter determines if the peer is being
@@ -855,9 +860,6 @@ enum ConnectingType {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::discovery::enr_ext::CombinedKeyExt;
-    use crate::rpc::methods::{MetaData, MetaDataV2};
-    use discv5::enr::CombinedKey;
     use slog::{o, Drain};
     use types::MinimalEthSpec as E;
 
@@ -880,23 +882,7 @@ mod tests {
             ..Default::default()
         };
         let log = build_log(slog::Level::Debug, false);
-        let globals = {
-            let keypair = libp2p::identity::Keypair::generate_secp256k1();
-            let enr_key: CombinedKey = CombinedKey::from_libp2p(&keypair).unwrap();
-            let enr = discv5::enr::EnrBuilder::new("v4").build(&enr_key).unwrap();
-            NetworkGlobals::new(
-                enr,
-                9000,
-                9000,
-                MetaData::V2(MetaDataV2 {
-                    seq_number: 0,
-                    attnets: Default::default(),
-                    syncnets: Default::default(),
-                }),
-                vec![],
-                &log,
-            )
-        };
+        let globals = NetworkGlobals::new_test_globals(&log);
         PeerManager::new(config, Arc::new(globals), &log)
             .await
             .unwrap()