Merge bitcoin/bitcoin#21914: net: use stronger AddLocal() for our I2P address

105941b726 net: use stronger AddLocal() for our I2P address (Vasil Dimov)

Pull request description:

  There are two issues:

  ### 1. Our I2P address not added to local addresses.

  * `externalip=` is used with an IPv4 address (this sets automatically `discover=0`)
  * No `discover=1` is used
  * `i2psam=` is used
  * No `externalip=` is used for our I2P address
  * `listenonion=1 torcontrol=` are used

  In this case `AddLocal(LOCAL_MANUAL)` [is used](94f83534e4/src/torcontrol.cpp (L354)) for our `.onion` address and `AddLocal(LOCAL_BIND)` [for our](94f83534e4/src/net.cpp (L2247)) `.b32.i2p` address, the latter being [ignored](94f83534e4/src/net.cpp (L232-L233)) due to `discover=0`.

  ### 2. Our I2P address removed from local addresses even if specified with `externalip=` on I2P proxy restart.

  * `externalip=` is used with our I2P address (this sets automatically `discover=0`)
  * No `discover=1` is used
  * `i2psam=` is used

  In this case, initially `externalip=` causes our I2P address to be [added](94f83534e4/src/init.cpp (L1266)) with `AddLocal(LOCAL_MANUAL)` which overrides `discover=0` and works as expected. However, if later the I2P proxy is shut down [we do](94f83534e4/src/net.cpp (L2234)) `RemoveLocal()` in order to stop advertising our I2P address (since we have lost I2P connectivity). When the I2P proxy is started and we reconnect to it, restoring the I2P connectivity, [we do](94f83534e4/src/net.cpp (L2247)) `AddLocal(LOCAL_BIND)` which does nothing due to `discover=0`.

  To resolve those two issues, use `AddLocal(LOCAL_MANUAL)` for I2P which is also what we do with Tor.

ACKs for top commit:
  laanwj:
    Code review ACK 105941b726

Tree-SHA512: 0c9daf6116b8d9c34ad7e6e9bbff6e8106e94e4394a815d7ae19287aea22a8c7c4e093c8dd8c58a4a1b1412b2575a9b42b8a93672c8d17f11c24508c534506c7

src/net.cpp

@@ -2245,7 +2245,7 @@ void CConnman::ThreadI2PAcceptIncoming()
         }
 
         if (!advertising_listen_addr) {
-            AddLocal(conn.me, LOCAL_BIND);
+            AddLocal(conn.me, LOCAL_MANUAL);
             advertising_listen_addr = true;
         }