- remove obsolete non-advanced-api support.
- if a routing entry exists for aggregate prefix (-A), do not overwrite
the routing entry (exit with error).
rip6query: RIPng query (similar to ripquery)
NOTE: we usually do not run route6d on end nodes at startup (rtsol should do
the trick). So I figured that route6d can be in /usr/sbin, not in /sbin
(routed is in /sbin). Correct me if I'm wrong.