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_windows.go

@@ -1,37 +1,36 @@
 // Code generated by go generate; DO NOT EDIT.
-// Generated: 2021-09-28 12:05:19.843209 +0200 CEST m=+0.079863168
+// Generated: 2021-09-28 18:13:54.317744 +0200 CEST m=+0.409422292
 
 package netxlite
 
 import "golang.org/x/sys/windows"
 
 const (
-	ECANCELED       = windows.ECANCELED
-	ECONNREFUSED    = windows.ECONNREFUSED
-	ECONNRESET      = windows.ECONNRESET
-	EHOSTUNREACH    = windows.EHOSTUNREACH
-	ETIMEDOUT       = windows.ETIMEDOUT
-	EAFNOSUPPORT    = windows.EAFNOSUPPORT
-	EADDRINUSE      = windows.EADDRINUSE
-	EADDRNOTAVAIL   = windows.EADDRNOTAVAIL
-	EISCONN         = windows.EISCONN
-	EFAULT          = windows.EFAULT
-	EBADF           = windows.EBADF
-	ECONNABORTED    = windows.ECONNABORTED
-	EALREADY        = windows.EALREADY
-	EDESTADDRREQ    = windows.EDESTADDRREQ
-	EINTR           = windows.EINTR
-	EINVAL          = windows.EINVAL
-	EMSGSIZE        = windows.EMSGSIZE
-	ENETDOWN        = windows.ENETDOWN
-	ENETRESET       = windows.ENETRESET
-	ENETUNREACH     = windows.ENETUNREACH
-	ENOBUFS         = windows.ENOBUFS
-	ENOPROTOOPT     = windows.ENOPROTOOPT
-	ENOTSOCK        = windows.ENOTSOCK
-	ENOTCONN        = windows.ENOTCONN
-	EWOULDBLOCK     = windows.EWOULDBLOCK
-	EACCES          = windows.EACCES
-	EPROTONOSUPPORT = windows.EPROTONOSUPPORT
-	EPROTOTYPE      = windows.EPROTOTYPE
+	ECONNREFUSED    = windows.WSAECONNREFUSED
+	ECONNRESET      = windows.WSAECONNRESET
+	EHOSTUNREACH    = windows.WSAEHOSTUNREACH
+	ETIMEDOUT       = windows.WSAETIMEDOUT
+	EAFNOSUPPORT    = windows.WSAEAFNOSUPPORT
+	EADDRINUSE      = windows.WSAEADDRINUSE
+	EADDRNOTAVAIL   = windows.WSAEADDRNOTAVAIL
+	EISCONN         = windows.WSAEISCONN
+	EFAULT          = windows.WSAEFAULT
+	EBADF           = windows.WSAEBADF
+	ECONNABORTED    = windows.WSAECONNABORTED
+	EALREADY        = windows.WSAEALREADY
+	EDESTADDRREQ    = windows.WSAEDESTADDRREQ
+	EINTR           = windows.WSAEINTR
+	EINVAL          = windows.WSAEINVAL
+	EMSGSIZE        = windows.WSAEMSGSIZE
+	ENETDOWN        = windows.WSAENETDOWN
+	ENETRESET       = windows.WSAENETRESET
+	ENETUNREACH     = windows.WSAENETUNREACH
+	ENOBUFS         = windows.WSAENOBUFS
+	ENOPROTOOPT     = windows.WSAENOPROTOOPT
+	ENOTSOCK        = windows.WSAENOTSOCK
+	ENOTCONN        = windows.WSAENOTCONN
+	EWOULDBLOCK     = windows.WSAEWOULDBLOCK
+	EACCES          = windows.WSAEACCES
+	EPROTONOSUPPORT = windows.WSAEPROTONOSUPPORT
+	EPROTOTYPE      = windows.WSAEPROTOTYPE
 )