BankingStage: set reasonable bound on max received packets per call

[apfitzge]

Problem

If the buffer is empty when many packets are in the sigverify channel, a single receive call may receive too many packets and lead to that thread missing a large fraction of a slot.

Summary of Changes

Bound the maxmimum number of packets to receive per call as 10k, or 2k if above half capacity.

Fixes #

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (5349308) 81.8% compared to head (7eed319) 81.8%. Report is 334 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #34622   +/-   ##
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  Coverage    81.8%    81.8%           
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  Files         824      824           
  Lines      222260   222263    +3     
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+ Hits       181910   181914    +4     
+ Misses      40350    40349    -1