net: ignore ports when comparing I2P addresses

From our perspective ports are ignored when connecting to the I2P
network. I.e. `aaa.b32.i2p:1111` is the same as `aaa.b32.i2p:2222`,
so compare them equal to avoid redundant connections to the same node if
ports happen to differ for some reason.

Fixes bitcoin#21389

src/netaddress.cpp

@@ -950,7 +950,14 @@ uint16_t CService::GetPort() const
 
 bool operator==(const CService& a, const CService& b)
 {
-    return static_cast<CNetAddr>(a) == static_cast<CNetAddr>(b) && a.port == b.port;
+    const bool addr_eq{static_cast<CNetAddr>(a) == static_cast<CNetAddr>(b)};
+    if (!addr_eq) {
+        return false;
+    }
+    if (a.IsI2P()) {
+        return true;
+    }
+    return a.port == b.port;
 }
 
 /**