addrman: reset I2P ports to 0 when loading from disk

This is a temporary change to convert I2P addresses that have propagated
with port 8333 to ones with port 0.

It would cause a problem some day if indeed some bitcoin software is
listening on port 8333 only and rejects connections to port 0 and we are
still using SAM 3.1 which only supports port 0. In this case we would
replace 8333 with 0 and try to connect to such nodes.

This commit should be included in 22.0 and be reverted before 23.0 is
released.

src/addrman.h

@@ -452,6 +452,8 @@ public:
 
         RemoveInvalid();
 
+        ResetI2PPorts();
+
         Check();
     }
 
@@ -767,6 +769,14 @@ private:
     //! Remove invalid addresses.
     void RemoveInvalid() EXCLUSIVE_LOCKS_REQUIRED(cs);
 
+    /**
+     * Reset the ports of I2P peers to 0.
+     * This is needed as a temporary measure because now we enforce port 0 and
+     * only connect to I2P hosts if the port is 0, but in the early days some
+     * I2P addresses with port 8333 were rumoured and persisted into addrmans.
+     */
+    void ResetI2PPorts() EXCLUSIVE_LOCKS_REQUIRED(cs);
+
     friend class CAddrManTest;
 };