Make the COB soft limit also use repl-backlog-size when its value is smaller

[enjoy-binbin]

We have the same settings for the hard limit, and we should apply them to the soft
limit as well. When the repl-backlog-size value is larger, all replication buffers
can be handled by the replication backlog, so there's no need to worry about the
client output buffer soft limit in here. Furthermore, when soft_seconds is 0, in
some ways, the soft limit behaves the same (mostly) as the hard limit.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.46%. Comparing base (8ea7f13) to head (16fa29f).

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #2866      +/-   ##
============================================
+ Coverage     72.44%   72.46%   +0.02%     
============================================
  Files           128      128              
  Lines         70415    70417       +2     
============================================
+ Hits          51011    51027      +16     
+ Misses        19404    19390      -14     

Files with missing lines	Coverage Δ
src/networking.c	88.44% <100.00%> (+<0.01%)	⬆️

... and 13 files with indirect coverage changes

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