Behaviorally this port should already be largely on par with the
NetBSD 8 version, in that it sets the RTF_LLDATA flag on routing
socket requests to indicate that they target link-local data.
Many parts of the arp(8) functionality are currently not yet supported
by the operating system, largely due to lwIP not exposing appropriate
means of implementing them.
Change-Id: Icfac054b4deddda03eee4acf0e261aa48cd031ba
