OpenVPNAdapter的呼叫

在除錯ios版openvpn的時候，在控制檯看到的出現的問題，連線失敗：

TUN Error: cannot acquire tun interface socket

參考：https://github.com/ss-abramchuk/OpenVPNAdapter/issues/37
原因：沒有讓packet通過，沒有設定setTunnelNetworkSettings
解決方法：修改或新增demo中extension PacketTunnelProvider: OpenVPNAdapterDelegate的方法：

    func openVPNAdapter(_ openVPNAdapter: OpenVPNAdapter, configureTunnelWithNetworkSettings networkSettings: NEPacketTunnelNetworkSettings, completionHandler: @escaping (OpenVPNAdapterPacketFlow?) -> Void) {
        setTunnelNetworkSettings(networkSettings) { (error) in
            completionHandler(error == nil ? self.packetFlow : nil)
        }
    }