health: don't look for UDP goroutines in js/wasm health check

Updates #3157

Change-Id: I43d97e6876eeb2d1936fc567835134568bb8615c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

health/health.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"runtime"
 	"sort"
 	"sync"
 	"sync/atomic"
@@ -347,6 +348,12 @@ var (
 	receiveFuncs = []*ReceiveFuncStats{&ReceiveIPv4, &ReceiveIPv6, &ReceiveDERP}
 )
 
+func init() {
+	if runtime.GOOS == "js" {
+		receiveFuncs = receiveFuncs[2:] // ignore IPv4 and IPv6
+	}
+}
+
 // ReceiveFuncStats tracks the calls made to a wireguard-go receive func.
 type ReceiveFuncStats struct {
 	// name is the name of the receive func.