i2p: log connection was refused due to arbitrary port

[brunoerg]

For I2P, we do not try to connect if port is != 0. However, we do not have anything that indicates it or any error when trying to connect with port != 0. This PR adds a log for it. Also, it improves the functional test. With this log we can ensure the reason we won't connect is the port, in the current test, we cannot ensure it.

[DrahtBot]

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ACK	jonatack, kristapsk, epiccurious, vasild, achow101

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[epiccurious]

Concept ACK 950f360.

[kristapsk]

cr utACK 950f360

[epiccurious]

Tested ACK 950f360.

[jonatack]

Approach ACK

[brunoerg]

Force-pushed addressing #29393 (comment)

[jonatack]

ACK 5b358cd

[kristapsk]

re-ACK 5b358cd

[epiccurious]

re-ACK 5b358cd.

[vasild]

ACK 5b358cd

How did you come to this? Did you encounter some !=0 I2P ports in the wild? I don't have any in my addrman:

$ bitcoin-cli getnodeaddresses 0 |jq 'map(select(.address |test("\\.i2p$"; "i"))) |map(select(.port != 0)) |length'
0

$ bitcoin-cli getnodeaddresses 0 |jq 'map(select(.address |test("\\.i2p$"; "i"))) |map(select(.port == 0)) |length'
1605

[brunoerg]

How did you come to this? Did you encounter some !=0 I2P ports in the wild?

I didn't encounter in practice, in fact, I was testing some nuances of i2p and tried to add it using addnode to check the behaviour, then I noticed that. Reading the functional test I realized that the way we were checking it was weird and did not really ensure the problem is the port.

[achow101]

ACK 5b358cd