Invalidate next-hop based on IPV4 ARP

This feature invalidates a static route based on the reachability of the next-hop in the ARP cache when the validate-next-hop command is enabled within the static-route-entry>next-hop context for an IPv4 static route.

In this case, when the ARP entry for the next-hop is INVALID or not populated, the static route must remain invalid/inactive. When an ARP entry for the next-hop is populated based on a gratuitous ARP received or periodic traffic destined for it and the usual ARP who-has procedure, the static route becomes valid/active and is installed.