DO NOT MERGE: Add a null check for the OnStartTetheringCallback.

This avoids a NullPointerException when trying to call the callback
and gives a more readable error message.

(cherry picked from commit 49a5795ef0c1e72a8d3637a6f25a8e14c2b330d8)

Change-Id: Ia419ff68ef10f308f9e44be47420e27099ee6070
1 file changed
tree: 9d9fcc800c397b4cd9885c533b958c71e483bf54
  1. core/
  2. services/
  3. tests/