hotfix(pmtud/tcp): fix code for IPv6 destinations

internal/pmtud/ip/ipv6_darwin.go

@@ -1,5 +0,0 @@
-package ip
-
-func SetIPv6HeaderIncluded(fd int) error {
-	panic("darwin does not allow an application to build IPv6 headers")
-}

internal/pmtud/ip/ipv6_linux.go

@@ -1,7 +0,0 @@
-package ip
-
-import "golang.org/x/sys/unix"
-
-func SetIPv6HeaderIncluded(fd int) error {
-	return unix.SetsockoptInt(fd, unix.IPPROTO_IPV6, unix.IPV6_HDRINCL, 1)
-}

internal/pmtud/ip/ipv6_unspecified.go

@@ -1,7 +0,0 @@
-//go:build !linux && !windows && !darwin
-
-package ip
-
-func SetIPv6HeaderIncluded(fd int) error {
-	panic("not implemented")
-}

internal/pmtud/ip/ipv6_windows.go

@@ -1,7 +0,0 @@
-package ip
-
-import "golang.org/x/sys/windows"
-
-func SetIPv6HeaderIncluded(fd windows.Handle) error {
-	panic("windows does not allow an application to build IPv6 headers")
-}

internal/pmtud/ip/source_unix.go

@@ -29,7 +29,7 @@ func makeSockAddr(ip netip.Addr, port uint16) unix.Sockaddr {
 		}
 	}
 	return &unix.SockaddrInet6{
-		Port: int(port),
+		Port: 0,
 		Addr: ip.As16(),
 	}
 }