Various fixes in IpReachability event logging

- fold IpReachabilityMonitor* classes into a single IpReachabilityEvent.
- only log an event for NUD_FAILED Netlink answers.
- distinguish between NUD_FAILED with or without lost of provisioning.
- do not record host ip addresses.
- record interface name instead of interface index when losing
  provisioning.

- also return an error code when probeNeighbor fails, and log this error
  code in IpReachability events.

Bug: 28204408
Change-Id: I5f0def0ab1ace7e467a0c69b3b82d07ef2252307