feature/portlist: pull portlist service porting into extension, use eventbus

And yay: tsnet (and thus k8s-operator etc) no longer depends on
portlist! And LocalBackend is smaller.

Removes 50 KB from the minimal binary.

Updates #12614

Change-Id: Iee04057053dc39305303e8bd1d9599db8368d926
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tsnet/tsnet_test.go

@@ -43,6 +43,7 @@ import (
 	"tailscale.com/net/netns"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tstest"
+	"tailscale.com/tstest/deptest"
 	"tailscale.com/tstest/integration"
 	"tailscale.com/tstest/integration/testcontrol"
 	"tailscale.com/types/key"
@@ -1302,3 +1303,15 @@ func mustDirect(t *testing.T, logf logger.Logf, lc1, lc2 *local.Client) {
 	}
 	t.Error("magicsock did not find a direct path from lc1 to lc2")
 }
+
+func TestDeps(t *testing.T) {
+	deptest.DepChecker{
+		GOOS:   "linux",
+		GOARCH: "amd64",
+		OnDep: func(dep string) {
+			if strings.Contains(dep, "portlist") {
+				t.Errorf("unexpected dep: %q", dep)
+			}
+		},
+	}.Check(t)
+}