Limit the number of initial peers

[oxarbitrage]

Motivation

We want to limit the number of initial peer attempts by config. Close #2900

Solution

Given the hashset of peers and a config parameter acting as the limit:

• convert the hashset to a vec.
• get a rand chunk from it using the standard library.
• convert back to hashset and use this from now on.

Review

Anyone can review. This is one of the security issues from created by @teor2345 for the beta.

[teor2345]

This looks good.

If you can think of an easy way to test it, we could add tests. But I can't think of any quick tests, and the code is simple enough, so we can merge without tests.

Let's merge after #2912 merges, because there are more tickets depending on #2912.

[teor2345]

I resolved conflicts and moved some more code out of zebra_network::initialize