Comment 9 for bug 2033980

So if radvd is stopped by the neutron l3-agent, it doesn't specify a signal and defaults to '9', so should always cleanup the pid file. But if it dies unexpectedly, or I believe if the l3-agent is restarted and restarts radvd for a network, there could be a stale pid file left behind.

Seems changing this code to be more like the keepalived code would solve the problem - when spawning the first thing it does is try and remove the pid file. I'll send a patch that does that which is pretty small, not sure if anyone has the means to test it to see if it helps in their environment.