[Tether] Log response code of unsuccessful TetherAvailabilityResponse.

This will help to more easily identify why users cannot find their
Tether hosts when they provide feedback reports.

Change-Id: Iff6d51f7e27eef36ed0312ba5c6ef61979ee8634
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900246
Auto-Submit: Ryan Hansberry <hansberry@chromium.org>
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712779}

chromeos/components/tether/host_scanner_operation.cc

@@ -199,7 +199,7 @@ void HostScannerOperation::OnMessageReceived(
       static_cast<TetherAvailabilityResponse*>(
           message_wrapper->GetProto().get());
   if (AreGmsCoreNotificationsDisabled(response)) {
-    PA_LOG(VERBOSE)
+    PA_LOG(WARNING)
         << "Received TetherAvailabilityResponse from device with ID "
         << remote_device.GetTruncatedDeviceIdForLogs() << " which "
         << "indicates that Google Play Services notifications are "
@@ -209,10 +209,11 @@ void HostScannerOperation::OnMessageReceived(
   } else if (!IsTetheringAvailableWithValidDeviceStatus(response)) {
     // If the received message is invalid or if it states that tethering is
     // unavailable, ignore it.
-    PA_LOG(VERBOSE)
+    PA_LOG(WARNING)
         << "Received TetherAvailabilityResponse from device with ID "
         << remote_device.GetTruncatedDeviceIdForLogs() << " which "
-        << "indicates that tethering is not available.";
+        << "indicates that tethering is not available. Response code: "
+        << response->response_code();
   } else {
     bool setup_required =
         response->response_code() ==