Switch to the system app context when using mobile data or wifi APIs

This will fix the case where tests are trying to use the mobile connection or wifi APIs when the current app context doesn't have access to them. I tried using SpecialPowers to grant such access but didn't have much luck - we could maybe revisit this later, but it would only cause an issue if we called any of these methods in the middle of a test. We could also switch back to the app context as a workaround.