Open items that need work on OpenNHRP:

- interface-up, nhs-up, nhs-down need to be serialized for quagga
  management. alternatively, the script could return some special
  value meaning "try again soon".

- offload multicast packet forwarding to kernel

- use mmapped pf_packet interface

- nhrp_peer should be split to more files, it's relatively large now.
  might split nhrp_peer to separate types.

- Proper handling of unique bit. Currently registration of unique address
  overwrites previous registration, but this against RFC.

- Load balancing: return multiple CIE entries, when we have multiple
  local IP addresses. When receiving multi CIE next-hop, balance traffic
  or for shortcut routes, create a multi nexthop route.

- Create some logic to detect if NBMA and public IPs are mixed up in
  the "map" directive. Issue on warning about this.

- Support reloading of configuration (via SIGHUP or "opennhrpctl reload")

- Clean shutdown: send purge request to registration servers, dynamic
  clients and possibly track resolution requests and purge those too.