Document a recipe for establishing SNMP tunnels using socat/SSH

[lunkwill42]

While developing new functionality related to SNMP collection in NAV, a developer's workstation isn't necessarily attached to a network that provides the developer with the necessary access to communicate with the require set of switches/routers etc. For internal equipment, this is usually solved by connection a VPN, but sometimes, the devices one needs to talk to are located at a customer site where there is no VPN access.

In our case, we often have SSH access to a Linux server at the customer premises - a server that is allowed to communicate with the customer's switches and routers. We have an internal recipe for how to establish a working SNMP tunnel to the customer's equipment using a combination of SSH and socat, but it would be advantageous to publish this recipe as part of NAV's hacking documentation.