ipn/ipnlocal: set the push device token correctly

It would end up resetting whatever hostinfo we had constructed
and leave the backend statemachine in a broken state.
This fixes that by storing the PushDeviceToken on the LocalBackend
and populating it on Hostinfo before passing it to controlclient.

Updates tailscale/corp#8940
Updates tailscale/corp#15367

Signed-off-by: Maisem Ali <maisem@tailscale.com>

hostinfo/hostinfo.go

@@ -53,7 +53,6 @@ func New() *tailcfg.Hostinfo {
 		GoVersion:       runtime.Version(),
 		Machine:         condCall(unameMachine),
 		DeviceModel:     deviceModel(),
-		PushDeviceToken: pushDeviceToken(),
 		Cloud:           string(cloudenv.Get()),
 		NoLogsNoSupport: envknob.NoLogsNoSupport(),
 		AllowsUpdate:    envknob.AllowsRemoteUpdate(),
@@ -166,18 +165,14 @@ func GetEnvType() EnvType {
 }
 
 var (
-	pushDeviceTokenAtomic atomic.Value // of string
-	deviceModelAtomic     atomic.Value // of string
-	osVersionAtomic       atomic.Value // of string
-	desktopAtomic         atomic.Value // of opt.Bool
-	packagingType         atomic.Value // of string
-	appType               atomic.Value // of string
-	firewallMode          atomic.Value // of string
+	deviceModelAtomic atomic.Value // of string
+	osVersionAtomic   atomic.Value // of string
+	desktopAtomic     atomic.Value // of opt.Bool
+	packagingType     atomic.Value // of string
+	appType           atomic.Value // of string
+	firewallMode      atomic.Value // of string
 )
 
-// SetPushDeviceToken sets the device token for use in Hostinfo updates.
-func SetPushDeviceToken(token string) { pushDeviceTokenAtomic.Store(token) }
-
 // SetDeviceModel sets the device model for use in Hostinfo updates.
 func SetDeviceModel(model string) { deviceModelAtomic.Store(model) }
 
@@ -203,11 +198,6 @@ func deviceModel() string {
 	return s
 }
 
-func pushDeviceToken() string {
-	s, _ := pushDeviceTokenAtomic.Load().(string)
-	return s
-}
-
 // FirewallMode returns the firewall mode for the app.
 // It is empty if unset.
 func FirewallMode() string {