like the remote nodes do, but for now do not update the up/down status
from that. I need to mess with db/node_status first to make sure there
is agreement between the parties. Note that remote nodes send one UDP
message every 60 seconds (isalive is done with a UDP). Local nodes
will send them at a slower rate, as is the practice in db/node_status
which wakes up every 5 minutes and fpings the world!