fix(net): Limit the number of leftover nonces in the self-connection nonce set

[teor2345]

Motivation

This PR prevents a memory exhaustion attack on Zebra.

It also limits the inbound connection rate to make similar attacks harder in future.

Complex Code or Requirements

This PR modifies concurrent network handshake code, where futures run concurrently.
It also adds more code to a futures mutex critical section.

It has already been reviewed privately by two Zebra developers.

Solution

• Limit the number of nonces in the nonce set to 500 or 8 kB the configured connection limit
• Limit the inbound connection rate to 1 per second
• Slightly decrease the outbound connection rate to one every 50 milliseconds

Review

This is ready for review. It needs to get merged before the next Zebra release.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
  • Does it change concurrent code, unsafe code, or consensus rules?
• How do you know it works? Does it have tests?

[arya2]

Is there a commit missing here?

[codecov]

Codecov Report

Merging #6534 (92bf9e3) into main (2e434b0) will increase coverage by 0.10%.
The diff coverage is 96.87%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6534      +/-   ##
==========================================
+ Coverage   77.68%   77.78%   +0.10%     
==========================================
  Files         305      306       +1     
  Lines       40104    40236     +132     
==========================================
+ Hits        31154    31298     +144     
+ Misses       8950     8938      -12     

[teor2345]

Is there a commit missing here?

Thanks for catching that, I forgot to fetch your tests before pushing the branch!