wgengine/netstack: add local tailscale service IPs to route and terminate locally (#18461)

* wgengine/netstack: add local tailscale service IPs to route and terminate locally

This commit adds the tailscales service IPs served locally to OS routes, and
make interception to packets so that the traffic terminates locally without
making affects to the HA traffics.

Fixes tailscale/corp#34048

Signed-off-by: KevinLiang10 <37811973+KevinLiang10@users.noreply.github.com>

* fix test

Signed-off-by: KevinLiang10 <37811973+KevinLiang10@users.noreply.github.com>

* add ready field to avoid accessing lb before netstack starts

Signed-off-by: KevinLiang10 <37811973+KevinLiang10@users.noreply.github.com>

* wgengine/netstack: store values from lb to avoid acquiring a lock

Signed-off-by: KevinLiang10 <37811973+KevinLiang10@users.noreply.github.com>

* add active services to netstack on starts with stored prefs.

Signed-off-by: KevinLiang10 <37811973+KevinLiang10@users.noreply.github.com>

* fix comments

Signed-off-by: KevinLiang10 <37811973+KevinLiang10@users.noreply.github.com>

* update comments

Signed-off-by: KevinLiang10 <37811973+KevinLiang10@users.noreply.github.com>

---------

Signed-off-by: KevinLiang10 <37811973+KevinLiang10@users.noreply.github.com>

tsd/tsd.go

@@ -32,6 +32,7 @@ import (
 	"tailscale.com/net/tstun"
 	"tailscale.com/proxymap"
 	"tailscale.com/types/netmap"
+	"tailscale.com/types/views"
 	"tailscale.com/util/eventbus"
 	"tailscale.com/util/syspolicy/policyclient"
 	"tailscale.com/util/usermetric"
@@ -111,6 +112,8 @@ type LocalBackend = any
 type NetstackImpl interface {
 	Start(LocalBackend) error
 	UpdateNetstackIPs(*netmap.NetworkMap)
+	UpdateIPServiceMappings(netmap.IPServiceMappings)
+	UpdateActiveVIPServices(views.Slice[string])
 }
 
 // Set is a convenience method to set a subsystem value.