Static neighbor support

This changes adds support for assigning static ARP / NDP
neighbors on each ethernet interface.

Tested:
    Ran inside a romulus VM and made sure that `ip neigh add`
    commands triggered the refresh of static_neighbor objects.
    Also verified that static neighbors could be added through
    the CreateStatic dbus interface. Verified that deleting those
    static entries would persist to the system.

Change-Id: Ifaf753525c532b6dade392d7eb4ebd6d7242d480
Signed-off-by: William A. Kennington III <wak@google.com>
9 files changed