do not treat WSAECONNRESET as a fatal error (#468)

[maxtomilov]

treating WSAECONNRESET as a fatal error for UDP socket causes IPE when e.g. trying to connect to not responding SRT peer.

[ethouris]

@rndi , this is ok to merge.

[alexpokotilo]

Hi @rndi, do you have any questions or concerns about this commit ?

[rndi]

Hi @alexpokotilo , yes, ideally I would like to better understand the reasons for the differences observed between Windows and Linux in this scenario before introducing this change, as per discussions in #468. Will probably need to write a bit of test code to validate current assumptions.

[alexpokotilo]

Do you expect anything from our team during this investigation?
Now Windows async SRT version doesn't work so you really need to add some tests to the project and probably confirm|change some assumptions about Windows|Linux differences. E.g this issue was found by UT in our project. We can send you our SRT unit tests if you want. We use google unit test so you can change our tests to fit your needs.
I just want to confirm that the ball is on your side and you don't wait for anything from us.

[rndi]

Hello @alexpokotilo , the ball is definitely on our side, no worries :) I've put together a small test and by the looks of it, I am able to replicate your results on Linux which is what I needed. I will get back to you on this.

If you think you can open a separate PR with some of your google unit tests included (and, preferably, enabled with CMake) that will probably be the best way to get that added to the project.