I2CP: Prevent loopback messages to same session (i2pd Github #2005)

core/java/src/net/i2p/client/impl/MessageState.java

@@ -157,6 +157,7 @@ class MessageState {
             case MessageStatusMessage.STATUS_SEND_FAILURE_EXPIRED_LEASESET:
             case MessageStatusMessage.STATUS_SEND_FAILURE_NO_LEASESET:
             case MessageStatusMessage.STATUS_SEND_FAILURE_META_LEASESET:
+            case MessageStatusMessage.STATUS_SEND_FAILURE_LOOPBACK:
             case SendMessageStatusListener.STATUS_CANCELLED:
                 // does not trump success
                 if (_state != State.SUCCESS)

core/java/src/net/i2p/data/i2cp/MessageStatusMessage.java

@@ -189,6 +189,13 @@ public class MessageStatusMessage extends I2CPMessageImpl {
      */
     public final static int STATUS_SEND_FAILURE_META_LEASESET = 22;
 
+    /**
+     *  Message was attempted to be sent to the same Destination.
+     *  This is a guaranteed failure.
+     *  @since 0.9.62
+     */
+    public final static int STATUS_SEND_FAILURE_LOOPBACK = 23;
+
     // NOTE:
     // Add any new status codes to handlers in:
     // net.i2p.client.impl.MessageState