vty: ns2: allow to disable most of the vty options for the pcu
The PCU should only get NS configuration via the info indication from BTS/BSC. Disable all configuration except the option to select sns or ipa style connect.
I'm not sure we really need to disable it. We have similar situations in other cases, like the SS7 configuration. All of it is always enabled, even though the BSC and MSC have "reasonable defaults" for the simple use case, and they use the "simple client".
What we must of course prevent is to save any configuration that has not been explicitly set by the user via VTY at "write file" time. Is that why you marked this as "urgent"?