txHandler: do not drop accepted mgs

[algorandskiy]

Summary

The (!isCMEnabled && congestedERL) condition in incomingMsgErlCheck added at some point to relief the spam congestion has the following side effect when:

1. per-peer reserved queue in ERL get exhausted
2. ERL's congestion manager (isCMEnabled) not enabled yet (it will be after the current ConsumeCapacity invocation)
3. shared capacity in ConsumeCapacity was successfully consumed

In this case the condition (!isCMEnabled && congestedERL) triggers congestion control to be enabled and dropping this message. In the same time consecutive messages would come through because isCMEnabled is set and erl.cm.ShouldDrop(c) might allow it due to messages rate.

Fixed by enabling congestion control but accepting the message if (!isCMEnabled && congestedERL) is met.

Note to reviewers:

This fix came out from ERL work and is is also integrated into the ERL change #6176

Test Plan

Rely on existing tests

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 51.77%. Comparing base (8fce49c) to head (2805a8d).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
data/txHandler.go	0.00%	1 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6257      +/-   ##
==========================================
- Coverage   51.79%   51.77%   -0.02%     
==========================================
  Files         644      644              
  Lines       86511    86512       +1     
==========================================
- Hits        44805    44794      -11     
- Misses      38834    38846      +12     
  Partials     2872     2872              

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