Allow setting I2P addresses #20662

This PR allows setting CNetAddr instances with I2P addresses by extending the existing method CNetAddr::SetSpecial.

Currently the method SetSpecial can be used with Tor addresses only. After this PR the same method can be used to set traditional I2P base 32 address (those with suffix .b32.i2p)

@lontivero Have you had a look at #20254? It may be a good idea to share ideas/review each other.

@jonatack i wasn't aware of #20254. I will close this one then. Thank you.

@lontivero Oh, to be clear I wasn't suggesting to close it but to review the other one and help each other.

Saw your review of #20254 -- that's great. Hope i2p support can move forward.

This functionality (with very similar diff) is included in #20685 as commit net: extend CNetAddr::SetSpecial() to support I2P.

I think it makes very little impact on its own - it makes Lookup() support I2P addresses, which in turn makes it possible to manually connect to an I2P node by using -proxy=i2p_socks5_proxy:port -addnode=i2p_address.b32.i2p:port.

But using the socks5 proxy in I2P usually means only being able to reach I2P peers and is discouraged.

#20685 already contains these changes.