Add log message to forwarder2's DeviceController when a port is unmapped.

tools/android/forwarder2/device_controller.cc

Index: tools/android/forwarder2/device_controller.cc
diff --git a/tools/android/forwarder2/device_controller.cc b/tools/android/forwarder2/device_controller.cc
index a6d370b67655634b9553b037a516af1ffefb8661..eda5868213cce22b2b29ecaef26bcc92dd613fe2 100644
--- a/tools/android/forwarder2/device_controller.cc
+++ b/tools/android/forwarder2/device_controller.cc
@@ -119,7 +119,9 @@ void DeviceController::AcceptHostCommandInternal() {
       listener->SetAdbDataSocket(socket.Pass());
       break;
     case command::UNLISTEN:
+      LOG(INFO) << "Unmapping port " << port;
       if (!listener) {
+        LOG(ERROR) << "No listener found for port " << port;
         SendCommand(command::UNLISTEN_ERROR, port, socket.get());
         break;
       }