NIC should be up, after VPP configure

[GeorgeGuo2018]

https://github.com/contiv/vpp/blob/master/docs/setup/VPP_CONFIG.md#multi-nic-configuration

In the VPP_CONFIG.md, there is a step to down a NIC which is chosed to allocated to VPP before config it.
After finish config this nic with VPP, I think there need a step to up it.