GGSN: Document how 'ip tuntap' is used for non-root; call netdev 'apn0'

* Some people want to manually create/configure their tun devices,
  show them how to do this using ip with the correct parameters
* Let's not call the network device 'ggsn' but rather 'apn0', as
  the device has a 1:1 correspondence to the APN, not to the GGSN.

Change-Id: I2fef818bfcb8cb521397136539f492922d5f6def
1 file changed
tree: 265637b4eb4d18f3872e75bd1cc728a7d4e937da
  1. doc/