p2p/nat: use IP.IsPrivate

[ucwong]

No description provided.

[codecov]

Codecov Report

Merging #1368 (ea40615) into master (2a60fcd) will increase coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1368      +/-   ##
==========================================
+ Coverage   51.65%   51.66%   +0.01%     
==========================================
  Files         461      461              
  Lines       58044    58044              
==========================================
+ Hits        29983    29990       +7     
  Misses      25785    25785              
+ Partials     2276     2269       -7     

Impacted Files	Coverage Δ
p2p/nat/natpmp.go	0.00% <0.00%> (ø)
p2p/discover/table.go	84.19% <0.00%> (-2.44%)	⬇️
ctxc/sync.go	60.00% <0.00%> (-1.30%)	⬇️
whisper/whisperv6/whisper.go	54.01% <0.00%> (-1.20%)	⬇️
ctxc/filters/api.go	50.66% <0.00%> (-0.67%)	⬇️
trie/proof.go	75.45% <0.00%> (-0.61%)	⬇️
ctxc/downloader/downloader.go	76.55% <0.00%> (-0.32%)	⬇️
p2p/discover/v5_udp.go	81.37% <0.00%> (+0.22%)	⬆️
p2p/simulations/network.go	60.57% <0.00%> (+0.71%)	⬆️
core/txpool/txpool.go	73.55% <0.00%> (+0.72%)	⬆️
... and 6 more