fix: don't use invalid port 0 when NATMap fails

[wlynxg]

fix: #3057

[sukunrt]

Thanks for the PR @wlynxg

[sukunrt]

Remove the check from here.

[sukunrt]

Add the port 0 check to line 911 where we check for is unspecified address. If you do so, it removes the need for introducing this new successMapCnt variable.

I would prefer keeping this change small because this code is pretty bad and we intend to rewrite it soon in #2229

[wlynxg]

Does the check placed on line 911 mean that the continue is executed when the extMaddr port is 0? If so, when all extMaddr ports are 0, will observedAddrs not be added to the finalAddrs address list?

[sukunrt]

I don't think so.

		if !manet.IsIPUnspecified(extMaddr) {
				// Add in the mapped addr.
				finalAddrs = append(finalAddrs, extMaddr)
} else {

If the nat provided address is not an unspecified addr and(new change) it's not port == 0, we will add it to final addrs.
We still fall through and add the observed addresses.

[wlynxg]

It is OK to add the address whose port is not 0 to finalAddrs here.

However, at

go-libp2p/p2p/host/basic/basic_host.go

Line 952 in f421202

finalAddrs = append(finalAddrs, ma.Join(ip, extMaddrNoIP))

, it is also necessary to judge whether the port is 0. If the port is 0, should the obsMaddr address be added directly without splicing?