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/ip/source_unix.go

@@ -0,0 +1,51 @@
+//go:build linux || darwin
+
+package ip
+
+import (
+	"fmt"
+	"net/netip"
+
+	"golang.org/x/sys/unix"
+)
+
+func socket(domain int, typ int, proto int) (fd int, err error) {
+	return unix.Socket(domain, typ, proto)
+}
+
+func closeSocket(fd int) error {
+	return unix.Close(fd)
+}
+
+func bind(fd int, addr unix.Sockaddr) error {
+	return unix.Bind(fd, addr)
+}
+
+func makeSockAddr(ip netip.Addr, port uint16) unix.Sockaddr {
+	if ip.Is4() {
+		return &unix.SockaddrInet4{
+			Port: int(port),
+			Addr: ip.As4(),
+		}
+	}
+	return &unix.SockaddrInet6{
+		Port: int(port),
+		Addr: ip.As16(),
+	}
+}
+
+func extractPortFromFD(fd int) (uint16, error) {
+	sockAddr, err := unix.Getsockname(fd)
+	if err != nil {
+		return 0, fmt.Errorf("getting sockname: %w", err)
+	}
+
+	switch typedSockAddr := sockAddr.(type) {
+	case *unix.SockaddrInet4:
+		return uint16(typedSockAddr.Port), nil //nolint:gosec
+	case *unix.SockaddrInet6:
+		return uint16(typedSockAddr.Port), nil //nolint:gosec
+	default:
+		panic(fmt.Sprintf("unexpected sockaddr type: %T", typedSockAddr))
+	}
+}