bug: prevent drop from bootstrap peers right after connection

[weboko]

Description

After investigating js-waku bootstrap it became clear that js-waku drops connection to second bootstrap peer right after it get's connected.

Reason for this is because of following factors:

• pruning of bootstrap connections is implemented in peer:connect event - here
• max bootstrap peers to keep is set to 1

Solution

Implement an interval check to keep checking if limits are respected.
This way we will keep bootstrap peers for longer and thus discover network better.
Second part is to increase amount of max bootstrap peers to 3 (just random number).