util/usermetrics: make usermetrics non-global

this commit changes usermetrics to be non-global, this is a building
block for correct metrics if a go process runs multiple tsnets or
in tests.

Updates #13420
Updates tailscale/corp#22075

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

wgengine/userspace.go

@@ -49,6 +49,7 @@ import (
 	"tailscale.com/util/mak"
 	"tailscale.com/util/set"
 	"tailscale.com/util/testenv"
+	"tailscale.com/util/usermetric"
 	"tailscale.com/version"
 	"tailscale.com/wgengine/capture"
 	"tailscale.com/wgengine/filter"
@@ -195,6 +196,9 @@ type Config struct {
 	// HealthTracker, if non-nil, is the health tracker to use.
 	HealthTracker *health.Tracker
 
+	// Metrics, if non-nil, is the usermetrics registry to use.
+	Metrics *usermetric.Registry
+
 	// Dialer is the dialer to use for outbound connections.
 	// If nil, a new Dialer is created.
 	Dialer *tsdial.Dialer
@@ -249,6 +253,8 @@ func NewFakeUserspaceEngine(logf logger.Logf, opts ...any) (Engine, error) {
 			conf.ControlKnobs = v
 		case *health.Tracker:
 			conf.HealthTracker = v
+		case *usermetric.Registry:
+			conf.Metrics = v
 		default:
 			return nil, fmt.Errorf("unknown option type %T", v)
 		}
@@ -289,9 +295,9 @@ func NewUserspaceEngine(logf logger.Logf, conf Config) (_ Engine, reterr error)
 
 	var tsTUNDev *tstun.Wrapper
 	if conf.IsTAP {
-		tsTUNDev = tstun.WrapTAP(logf, conf.Tun)
+		tsTUNDev = tstun.WrapTAP(logf, conf.Tun, conf.Metrics)
 	} else {
-		tsTUNDev = tstun.Wrap(logf, conf.Tun)
+		tsTUNDev = tstun.Wrap(logf, conf.Tun, conf.Metrics)
 	}
 	closePool.add(tsTUNDev)
 
@@ -387,6 +393,7 @@ func NewUserspaceEngine(logf logger.Logf, conf Config) (_ Engine, reterr error)
 		NoteRecvActivity: e.noteRecvActivity,
 		NetMon:           e.netMon,
 		HealthTracker:    e.health,
+		Metrics:          conf.Metrics,
 		ControlKnobs:     conf.ControlKnobs,
 		OnPortUpdate:     onPortUpdate,
 		PeerByKeyFunc:    e.PeerByKey,