drvAsynIPPort depends on EWOULDBLOCK being the same as EAGAIN

[ericonr]

This conditional in readIt() is used to determine if we should disconnect from the device. It seems to rely on EWOULDBLOCK being the same as EAGAIN (since recv/recvfrom can return either of them), which is not a guarantee -- though I don't know if it's actually the case for any platform. I wouldn't be surprised if a lot of code (in general and EPICS code specifically) relies on this assumption, but the Linux manuals recommend against it explicitly as well (under ERRORS).

From https://epics.anl.gov/tech-talk/2023/msg00466.php