Failure to handle keepalive packets explicitely cause issues with Cisco and f5 devices

we fixed this internally by addding the following to the SshChannel.cs file in the OnRequestReceived function.

        //NOTE (VAE): This prevents wrong things from happening because of a failure to handle ssh keepalive requests, seen on Cisco Wireless and F5 Network devices
        case "keepalive@openssh.com":
            if (!_closeSent)
            {
                Session.KeepAlive();
            }
            break;
        // VAE