Optimize download strategy and parameters

[Junyu Liu]

The default parameters are consistent with the official client to reduce the probability of blocking

https://github.com/telegramdesktop/tdesktop/blob/dev/Telegram/SourceFiles/export/export_api_wrap.cpp#L25-L26

https://github.com/DrKLO/Telegram/blob/master/TMessagesProj/src/main/java/org/telegram/messenger/FileLoadOperation.java#L81-L87

[Junyu Liu]

adf4edc