tsd: wire up the event bus to tailscaled

Updates #15160

Signed-off-by: David Anderson <dave@tailscale.com>

cmd/tailscaled/tailscaled.go

@@ -62,6 +62,7 @@ import (
 	"tailscale.com/types/logger"
 	"tailscale.com/types/logid"
 	"tailscale.com/util/clientmetric"
+	"tailscale.com/util/eventbus"
 	"tailscale.com/util/multierr"
 	"tailscale.com/util/osshare"
 	"tailscale.com/version"
@@ -376,6 +377,10 @@ func run() (err error) {
 
 	sys := new(tsd.System)
 
+	// Install an event bus as early as possible, so that it's
+	// available universally when setting up everything else.
+	sys.Set(eventbus.New())
+
 	// Parse config, if specified, to fail early if it's invalid.
 	var conf *conffile.Config
 	if args.confFile != "" {