OsmoGGSN: more info on non-root operation / tun creation

Add examples for 'ip addr add' and mention correspondence to config file,
add examples for enabling masquerading and IP forwarding,
place the non-root config in its own section and highlight the diffs.

Add tiny hint at systemd-networkd.

Change-Id: I02bd9cfa35c7f2fb338d5d92c2e968fe80574a78
1 file changed
tree: 60db7c5ca054bf019ca8ef04fa10960ae54c021f
  1. doc/