3G flag settings for other downloads

Currently, in the UDM downloader, the allow_gsm flag is set on all downloads based on the auto_download value. If that value is != 1 (where 0 == manual, 1 == auto, 2 == wifi only) then allow_gsm will be set, otherwise it will be unset. This may not always be what you want.

If an explicit manual download is initiated, then arguably allow_gsm should be set to true, under the assumption that if the user is on gsm-only and they've explicitly asked for a download or check, it should go through.

Also, allow_gsm should possibly be set for the CheckForUpdate, regardless of whether it was explicit or not, since checks are fairly cheap compared to updates (although also downloading key files increases the data usage).

I wonder if changes here require design sign-off?