mininet自带版本过低，可以将ovs升级到最新版本

1.Remove old packages

sudo apt-get remove openvswitch-common openvswitch-datapath-dkms openvswitch-controller openvswitch-pki openvswitch-switch

2.安装ovs 2.3.0(参考 安装openvswitch 2.3.0)

Update to openvswitch 2.3.0