[Provider Model] Fix WiFi list count timing issue (QS Internet Dialog)

- The WiFi list count will be updated when the WiFi scan result is
called back, but it needs to be reduced immediately after turning off
the airplane mode.

- See b/206807144#comment12 for a video.

Bug: 206807144
Test: manual test
atest -c InternetAdapterTest \
         InternetDialogTest

Change-Id: I6082226a63808e8a532bf4e9f341800a1887b8f5