olsrd plugin: Add a plugin for the “optimized link-state routing daemon”.

olsrd plugin: Add a plugin for the “optimized link-state routing daemon”.

This daemon is often used to route in mesh networks, i. e. highly dynamic
wireless networks. The plugin connects to the TCP port opened by the `txtinfo'
plugin of olsrd and parses its output.

Available statistics are:

  * links: How many direct connections exist and which quality do they have?
  * routes: Number of nets/hosts a node can contact and the average metric to
    each network.
  * topology: Link quality of the entire topology known to the router.

Each statistic can be configured to be collected as

  * No:      Values are ignored.
  * Summary: Only a fixed number of statistics are collected. This number does
             *not* depend on the number of nodes in the network.
  * Detail:  One (or more) values for each link/node, i. e. the number of
             values depends on the number of hosts and may be *huge*.

No documentation exists yet. The plugin has not yet been tested.