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/constants/syscall_unix.go

@@ -0,0 +1,16 @@
+//go:build linux || darwin
+
+package constants
+
+import "golang.org/x/sys/unix"
+
+//nolint:revive
+const (
+	SOCK_RAW    = unix.SOCK_RAW
+	SOCK_STREAM = unix.SOCK_STREAM
+	AF_INET     = unix.AF_INET
+	AF_INET6    = unix.AF_INET6
+	IPPROTO_TCP = unix.IPPROTO_TCP
+	EAGAIN      = unix.EAGAIN
+	EWOULDBLOCK = unix.EWOULDBLOCK
+)

internal/pmtud/constants/syscall_windows.go

@@ -0,0 +1,13 @@
+package constants
+
+import "golang.org/x/sys/windows"
+
+const (
+	SOCK_RAW    = windows.SOCK_RAW
+	SOCK_STREAM = windows.SOCK_STREAM
+	AF_INET     = windows.AF_INET
+	AF_INET6    = windows.AF_INET6
+	IPPROTO_TCP = windows.IPPROTO_TCP
+	EAGAIN      = windows.WSAEWOULDBLOCK
+	EWOULDBLOCK = windows.WSAEWOULDBLOCK
+)