config for disabling NAT port mapping

[magik6k]

Should give users a way to address issues like #2571

[codecov]

Codecov Report

Merging #7204 (3708a7a) into master (982a377) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #7204   +/-   ##
=======================================
  Coverage   39.19%   39.19%           
=======================================
  Files         608      608           
  Lines       64559    64559           
=======================================
+ Hits        25302    25307    +5     
+ Misses      34877    34872    -5     
  Partials     4380     4380           

Impacted Files	Coverage Δ
node/builder.go	83.70% <ø> (ø)
chain/actors/builtin/paych/paych.go	16.88% <0.00%> (-5.20%)	⬇️
extern/sector-storage/sched_worker.go	76.53% <0.00%> (-1.45%)	⬇️
chain/sync_manager.go	66.77% <0.00%> (-0.94%)	⬇️
chain/messagepool/selection.go	80.52% <0.00%> (-0.82%)	⬇️
extern/storage-sealing/fsm.go	56.62% <0.00%> (-0.41%)	⬇️
chain/sync.go	61.20% <0.00%> (-0.22%)	⬇️
storage/wdpost_changehandler.go	98.58% <0.00%> (+0.94%)	⬆️
lib/rpcenc/reader.go	71.78% <0.00%> (+1.48%)	⬆️
extern/sector-storage/sched.go	84.71% <0.00%> (+1.65%)	⬆️
... and 3 more

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[arajasek]

Nice comments!