Account for stack differences in the socketpair test (issue #312)

[haesbaert]

Linux returns ECONNRESET while every other stack tested returns EOF on this test.

I did not dig into the especification but Linux appears to be on the weird side.

In order to get a ECONNRESET, the write needs to hit the socket after the close, but our program does:

WRITE(A)
CLOSE(B)
READ(A)

Linux never gives "A" side a chance to see a proper EOF, while the others do:

Linux -> ECONNRESET
FreeBSD 12 -> EOF
OpenBSD 7.2 -> EOF
macos 12.5.1 -> EOF

We can fix this by properly draining B side of things before the close, but we can't reliably test ECONNRESET so turn this into an EOF test for now.

[talex5]

The test is specifically trying to test for this error, though (i.e. where data may have been lost). I found some more info at https://stackoverflow.com/questions/2974021/what-does-econnreset-mean-in-the-context-of-an-af-local-socket

I suggest performing the same operations as before, but adding | End_of_file to allow that outcome too for non-Linux systems.

[talex5]

Thanks!