net: fix MIB_IF_ROW2 layout on Windows 386

net/net_windows.go

@@ -90,7 +90,6 @@ type guid struct {
 const (
 	maxStringSize        = 256
 	maxPhysAddressLength = 32
-	pad0for64_4for32     = 0
 )
 
 type mibIfRow2 struct {

net/net_windows_386.go

@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: BSD-3-Clause
+//go:build windows && 386
+
+package net
+
+const pad0for64_4for32 = 4

net/net_windows_386_test.go

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: BSD-3-Clause
+//go:build windows && 386
+
+package net
+
+import (
+	"testing"
+	"unsafe"
+)
+
+func TestMibIfRow2Layout(t *testing.T) {
+	var row mibIfRow2
+	if offset := unsafe.Offsetof(row.TransmitLinkSpeed); offset != 1192 {
+		t.Errorf("TransmitLinkSpeed offset = %d, want 1192", offset)
+	}
+	if size := unsafe.Sizeof(row); size != 1352 {
+		t.Errorf("mibIfRow2 size = %d, want 1352", size)
+	}
+}

net/net_windows_not386.go

@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: BSD-3-Clause
+//go:build windows && !386
+
+package net
+
+const pad0for64_4for32 = 0