address race condition in DHT initialization

[Vectorrent]

This PR is an attempt to address some kind of race condition that can occur during expert bootstrapping. I spent several hours trying to identify the source of the problem, only to fall-back to an easy solution - which doesn't actually address the underlying problem.

For some reason, calling dht.get_visible_maddrs(True) on the DHT node fixes the issue. So, that's what we do now - every time the DHT node is started.

Since using get_visible_maddrs apparently fixes the problem, we can assume that something this method does is important to expert initialization. Yet, the only thing this method does is use Multiaddr; and so, I can only assume that there must be some kind of failure in Multiaddr, somewhere else in the code.

This is far outside my area of expertise, and I spent a lot of time troubleshooting already - so this is the best solution I could figure out, for now.