[Merged by Bors] - p2p: add connection gater to prevent dials over max limit

[dshulyak]

closes: #4771

this change will reject dials from outbound peers when inbound number is 0.8 of high peers number.
it will not allow dials to other peers when total number of peers is higher then 1.1 of high peers number.
and node is allowed to always dial direct peers

note that dials are concurrent, so if there is a burst it is still possible that they will go over the limit for short period of time

[codecov]

Codecov Report

Merging #4775 (6717dae) into develop (6a4208b) will decrease coverage by 0.1%.
The diff coverage is 62.8%.

@@            Coverage Diff            @@
##           develop   #4775     +/-   ##
=========================================
- Coverage     76.8%   76.8%   -0.1%     
=========================================
  Files          259     260      +1     
  Lines        29491   29524     +33     
=========================================
+ Hits         22659   22678     +19     
- Misses        5392    5402     +10     
- Partials      1440    1444      +4     

Files Changed	Coverage Δ
p2p/host.go	37.0% <50.0%> (+2.7%)	⬆️
p2p/gater.go	80.0% <80.0%> (ø)

... and 2 files with indirect coverage changes

[pigmej]

1. Connections just sporadically go out of the high. 🟢
2. Direct peers are working even when high is exceeded 🟢

side note:
WITHOUT that patch my limits were ok when I did not have port forwarded (fewer peers connecting??), with port forwarded then limits were often exceeded but then it was going lower.

[dshulyak]

Connections just sporadically go out of the high

can you clarify this part? i expect them to go above high if node is making many concurrent dials, so for example you are at 80 peers, node make 50 dials at the same time, connections will to 130, but that should be rare. is it consistent with your observations or not at all?

[pigmej]

Yeah, more or less what you described. Sporadically going out of bounds and then quickly down.

[dshulyak]

bors try

[bors]

try

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[dshulyak]

bors merge

[bors]

Pull request successfully merged into develop.

Build succeeded!

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