portlist: add Poller.IncludeLocalhost option

This PR parameterizes receiving loopback updates from the portlist package.
Callers can now include services bound to localhost if they want.
Note that this option is off by default still.

Fixes #8171

Signed-off-by: Marwan Sulaiman <marwan@tailscale.com>

portlist/portlist_test.go

@@ -5,9 +5,7 @@ package portlist
 
 import (
 	"context"
-	"flag"
 	"net"
-	"runtime"
 	"sync"
 	"testing"
 	"time"
@@ -51,16 +49,9 @@ func TestIgnoreLocallyBoundPorts(t *testing.T) {
 	}
 }
 
-var flagRunUnspecTests = flag.Bool("run-unspec-tests",
-	runtime.GOOS == "linux", // other OSes have annoying firewall GUI confirmation dialogs
-	"run tests that require listening on the the unspecified address")
-
 func TestChangesOverTime(t *testing.T) {
-	if !*flagRunUnspecTests {
-		t.Skip("skipping test without --run-unspec-tests")
-	}
-
 	var p Poller
+	p.IncludeLocalhost = true
 	get := func(t *testing.T) []Port {
 		t.Helper()
 		s, err := p.getList()
@@ -71,7 +62,7 @@ func TestChangesOverTime(t *testing.T) {
 	}
 
 	p1 := get(t)
-	ln, err := net.Listen("tcp", ":0")
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
 	if err != nil {
 		t.Skipf("failed to bind: %v", err)
 	}