I have some suggestions:

  1. You need to check connectivity multiple times, not one time, which may be wrong. Generally you can check 3 times and no connectivity and then label it a no
  2. During boot, there is no internet yet, so this script execute quickly and then end. What you need to do is: (a) add detection of the easytethering interface. Only when there is easytether interface you start, otherwise you wait. (b) add some delay to execute this script after boot.