fix: allow to build miniooni for windows (#520)

I need to run test on Windows and I just discovered that:

1. the `errno_unix.go` filename does not mean anything because
`unix` is not a valid platform, so we need a filename for
each platform that we care about;

2. on Windows we need to use WSA prefixed names;

3. `i/e/session_psiphon.go` was not building because of the
migration from `netxlite/iox` to `netxlite`.

This diff attempts to fix all three issues.

The reference issue is https://github.com/ooni/probe/issues/1733,
because I was working on such an issue.

internal/netxlite/errno.go

@@ -1,5 +1,5 @@
 // Code generated by go generate; DO NOT EDIT.
-// Generated: 2021-09-28 12:05:19.868647 +0200 CEST m=+0.105301959
+// Generated: 2021-09-28 18:13:54.361886 +0200 CEST m=+0.453564501
 
 package netxlite
 
@@ -16,7 +16,6 @@ const (
 	//
 	// System errors
 	//
-	FailureOperationCanceled           = "operation_canceled"
 	FailureConnectionRefused           = "connection_refused"
 	FailureConnectionReset             = "connection_reset"
 	FailureHostUnreachable             = "host_unreachable"
@@ -67,7 +66,6 @@ const (
 // failureMap lists all failures so we can match them
 // when they are wrapped by quic.TransportError.
 var failuresMap = map[string]string{
-	"operation_canceled":             "operation_canceled",
 	"connection_refused":             "connection_refused",
 	"connection_reset":               "connection_reset",
 	"host_unreachable":               "host_unreachable",
@@ -120,8 +118,6 @@ func classifySyscallError(err error) string {
 		return ""
 	}
 	switch errno {
-	case ECANCELED:
-		return FailureOperationCanceled
 	case ECONNREFUSED:
 		return FailureConnectionRefused
 	case ECONNRESET: