Handle the case with too many DNS rules gracefully

[Zsombe]

In AdGuard iOS when the sum of all DNS rules exceeds approximately 535000 rules. WiFI crashes when this number of rules is exceeded.

[ameshkov]

DnsLibs notifies AdGuard that the engine exceeds the maximum allowed memory limit and it then forcibly stops the tunnel, this may look like a Wi-Fi crash because the tunnel is then restarted due to an "on demand" rule.

The solution would be to start the tunnel anyway with a limited engine instance and notify the user about that via a normal OS notification. The error code that should be used is AGDPE_MEM_LIMIT_REACHED.

[Greigh]

I have this issue on cellar, as well. It just breaks the data functionality of my phone completely. Will 4.6 fix this as well?

[ameshkov]

It will work, but it does not mean that it's a good idea to use a blocklist that's heavier than the limit as all rules above the limit will be discarded.