[pingpong] skip addPeer for ping message handler

Validator will receive peer info from pong message
sent by the leader, no need for validator to handle ping message to add
peer's pubkeys

Signed-off-by: Leo Chen <leo@harmony.one>

node/node_handler.go

@@ -388,9 +388,10 @@ func (node *Node) pingMessageHandler(msgPayload []byte, sender string) int {
 		return 0
 	}
 
-	// Add to Node's peer list anyway
-	utils.GetLogInstance().Info("Add Peer to Node", "Node", node.Consensus.GetNodeID(), "Pear", peer)
-	node.AddPeers([]*p2p.Peer{peer})
+	if node.NodeConfig.IsLeader() {
+		utils.GetLogInstance().Info("Add Peer to Node", "Node", node.Consensus.GetNodeID(), "Pear", peer)
+		node.AddPeers([]*p2p.Peer{peer})
+	}
 
 	return 1
 }