chore(pmtud): remove calls to syscall in favor of unix and windows

- syscall is deprecated and is not kept up-to-date
- each OS is inherently different hence the syscall being deprecated

internal/pmtud/icmp/df_windows.go

@@ -1,11 +1,11 @@
 package icmp
 
 import (
-	"syscall"
+	"golang.org/x/sys/windows"
 )
 
 func setDontFragment(fd uintptr) (err error) {
 	// https://docs.microsoft.com/en-us/troubleshoot/windows/win32/header-library-requirement-socket-ipproto-ip
 	// #define IP_DONTFRAGMENT        14     /* don't fragment IP datagrams */
-	return syscall.SetsockoptInt(syscall.Handle(fd), syscall.IPPROTO_IP, 14, 1)
+	return windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IP, 14, 1)
 }