p2p/nat: handle responses with alternative port in NAT-PMP

[ucwong]

Co-authored-by: Felix Lange fjl@twurst.com

[codecov]

Codecov Report

Merging #1379 (ba378e8) into master (bc2fcc9) will increase coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1379      +/-   ##
==========================================
+ Coverage   51.59%   51.60%   +0.01%     
==========================================
  Files         461      461              
  Lines       58058    58063       +5     
==========================================
+ Hits        29954    29965      +11     
+ Misses      25834    25826       -8     
- Partials     2270     2272       +2     

Impacted Files	Coverage Δ
p2p/nat/natpmp.go	0.00% <0.00%> (ø)
accounts/keystore/watch.go	91.66% <0.00%> (-4.17%)	⬇️
p2p/simulations/mocker.go	34.54% <0.00%> (-2.73%)	⬇️
ctxc/sync.go	60.00% <0.00%> (-1.30%)	⬇️
p2p/peer.go	74.16% <0.00%> (-0.84%)	⬇️
core/txpool/txpool.go	72.58% <0.00%> (-0.73%)	⬇️
p2p/discover/v5_udp.go	81.15% <0.00%> (-0.23%)	⬇️
ctxc/downloader/downloader.go	77.38% <0.00%> (-0.11%)	⬇️
core/rawdb/freezer.go	42.61% <0.00%> (ø)
ctxc/peer.go	68.59% <0.00%> (+0.55%)	⬆️
... and 4 more