drop connection data if a client has closed the connection via RST\FIN

[RomanBelozerov]

Motivation

A large memory consumption was noticed when testing 38 issue (DDoS mitigation testing). One of the problems that requires investigation - getting TCP FIN\RST in a connection while processing data of this connection. TempestaFW should drop connection data and free up memory as soon as possible. Nginx has 499 status code in access log for this case.

Case example:

1. a client open http1\h2 connection and send a request;
2. TempestaFW forwards the request to a upstream or finds a response in cache;
3. the client sends TCP FIN\RST before sending the response from TempestaFW;

Expected behaviour - TempestaFW drops connection data and free up memory as soon as possible. Probably, we cannot drop connection data just like that because we must count the number of requests for frang limits (request_rate and request_burst).

Testing

Please create a test issue or add http1\h2 tests to tempesta-test.

Documentation

We should add info about this behaviour in wiki