allow to use mobile network to backup photos

1. mobile network includes 2G/3G/4G.
2. only use WiFi to backup photos by default.
3. always use WiFi when both network types available.
Why turns off auto upload camera photos option just because the user canceled choosing library? Say the user has already turned it on for a while, and clicks "change the target library", then he just cancels from the library choosing activity, just to find auto upload is turned off, which is weird.