diff_drive_controller: lifecycle checks in update method

[christophfroehlich]

          This was in the old update() function and I kept it in because without it I failed tests (eg. "cleanup" in test_diff_drive_controller.cpp) that were calling update after deactivation. Whether or not to keep it depends on your philosophy: how much do you trust the external controller manager to not call update after deactivating the node?

Originally posted by @arthurlovekin in #1485 (comment)