Add placeholder methods for Send and Broadcast

Former-commit-id: fd78c149bb1b19439ed3a6b1f6036d8f381f2879 [formerly cdcc33a37eea0c297dbe05d21f2fcbbf38b1503e]
Former-commit-id: ee7a588c5eecdf3cf5b2e05191359d8cb7a8798c

sharding/p2p/service.go

@@ -31,3 +31,13 @@ func (s *Server) Stop() error {
 	log.Info("Stopping shardp2p server")
 	return nil
 }
+
+// Send a message to a specific peer.
+func (s *Server) Send(msg interface{}, Peer peer) {
+	// TODO
+}
+
+// Broadcast a message to the world.
+func (s *Server) Broadcast(msg interface{}) {
+	// TODO
+}