zebra: move neighbor table configuration to dplane contexts

zebra: move neighbor table configuration to dplane contexts

Instead of directly configuring the neighbor table after read from zapi
interface, a zebra dplane context is prepared to host the interface and
the family where the neighbor table is updated. Also, some other fields
are hosted: app_probes, ucast_probes, and mcast_probes. More information
on those fields can be found on ip-ntable configuration.

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>