wgengine/magicsock,net/sockopts: export Windows ICMP suppression logic (#16917)

For eventual use by net/udprelay.Server.

Updates tailscale/corp#31506

Signed-off-by: Jordan Whited <jordan@tailscale.com>

wgengine/magicsock/magicsock_windows.go

@@ -1,58 +0,0 @@
-// Copyright (c) Tailscale Inc & AUTHORS
-// SPDX-License-Identifier: BSD-3-Clause
-
-//go:build windows
-
-package magicsock
-
-import (
-	"net"
-	"unsafe"
-
-	"golang.org/x/sys/windows"
-	"tailscale.com/types/logger"
-	"tailscale.com/types/nettype"
-)
-
-func trySetUDPSocketOptions(pconn nettype.PacketConn, logf logger.Logf) {
-	c, ok := pconn.(*net.UDPConn)
-	if !ok {
-		// not a UDP connection; nothing to do
-		return
-	}
-
-	sysConn, err := c.SyscallConn()
-	if err != nil {
-		logf("trySetUDPSocketOptions: getting SyscallConn failed: %v", err)
-		return
-	}
-
-	// Similar to https://github.com/golang/go/issues/5834 (which involved
-	// WSAECONNRESET), Windows can return a WSAENETRESET error, even on UDP
-	// reads. Disable this.
-	const SIO_UDP_NETRESET = windows.IOC_IN | windows.IOC_VENDOR | 15
-
-	var ioctlErr error
-	err = sysConn.Control(func(fd uintptr) {
-		ret := uint32(0)
-		flag := uint32(0)
-		size := uint32(unsafe.Sizeof(flag))
-		ioctlErr = windows.WSAIoctl(
-			windows.Handle(fd),
-			SIO_UDP_NETRESET,               // iocc
-			(*byte)(unsafe.Pointer(&flag)), // inbuf
-			size,                           // cbif
-			nil,                            // outbuf
-			0,                              // cbob
-			&ret,                           // cbbr
-			nil,                            // overlapped
-			0,                              // completionRoutine
-		)
-	})
-	if ioctlErr != nil {
-		logf("trySetUDPSocketOptions: could not set SIO_UDP_NETRESET: %v", ioctlErr)
-	}
-	if err != nil {
-		logf("trySetUDPSocketOptions: SyscallConn.Control failed: %v", err)
-	}
-}