Kiss 'o Death packets are used by servers that need to throttle polling of heavily used servers. It's a feature of the NTP v4 protocol, allowing time servers to warn users to reduce their transmission rates to the server to prevent the servers from being overwhelmed. While there is so far nothing (that I can find anyway) explicit in NTP v4 that forces the client to throttle back requests, it's apparently implemented in your Netgear router.