Returns true if there is a [NetworkedMultiplayerPeer] set (with [method SceneTree.set_network_peer]).
Returns true if this SceneTree's [NetworkedMultiplayerPeer] is in server mode (listening for connections).
Set the peer object to handle the RPC system (effectively enabling networking). Depending on the peer itself, the SceneTree will become a network server (check with [method is_network_server()]) and will set root node's network mode to master (see NETWORK_MODE_* constants in [Node]), or it will become a regular peer with root node set to slave. All child nodes are set to inherit the network mode by default. Handling of networking-related events (connection, disconnection, new clients) is done by connecting to SceneTree's signals.