Setup refine

[minghu6]

There is no need to create manually /dev/net/tap each time. And the 10, 200 is the /dev/net/tun based on device.txt. So, sudo mknod /dev/net/tap c 10 200 is just creating an alias for tun/tap device. It's also confused since the kernel using IFF_TUN or IFF_TAP flag to distinguish Tun device or Tap device respectly instead of open /dev/net/tun or open /dev/net/tap.