Internet connectivity issues

[ignoramous]

I've hit internet drops with YouTube, Google Maps, and Telegram when other apps seemingly continue to work fine. This, peculiarly enough, has often happened on Mobile data (and never on WiFi).

Previous work on this #248 meant the app works hard to not restart the VPN in a bid to prevent leaking connections. Figure out if there's a race in how NetworkManager works with ConnectivityService because the API documentation explicitly warns of race when fetching Networks in the Callbacks?

Two possible workarounds whilst we figure out the root-cause:

1. Provide users with a knob to choose if the app should restart the VPN on every connectivity change like NetGuard does? Enable it by default, even?
2. May be the act of changing the underlying network on the VPN could be handed off to WorkManager to be done 5s and 10s after the fact whilst cancelling existing vpn work if any? Or may be, a simple android.os.Handler would suffice?

[ignoramous]

Ref: shadowsocks/shadowsocks-android@0af4500
Blog: https://archive.is/fQLNK
And: AdguardTeam/AdguardForAndroid#2836

[ignoramous]

We could also perhaps make use of android.net.ConnectivityDiagnosticsManager to be notified of data-stalls and connectivity-probe reports on API Level 30+

[ignoramous]

#282