wgengine/router: rely on events for deleted IP rules (#16744)

Adds the eventbus to the router subsystem.

The event is currently only used on linux.

Also includes facilities to inject events into the bus.

Updates #15160

Signed-off-by: Claus Lensbøl <claus@tailscale.com>

wgengine/router/router.go

@@ -14,6 +14,7 @@ import (
 	"tailscale.com/net/netmon"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/preftype"
+	"tailscale.com/util/eventbus"
 )
 
 // Router is responsible for managing the system network stack.
@@ -45,9 +46,11 @@ type Router interface {
 //
 // If netMon is nil, it's not used. It's currently (2021-07-20) only
 // used on Linux in some situations.
-func New(logf logger.Logf, tundev tun.Device, netMon *netmon.Monitor, health *health.Tracker) (Router, error) {
+func New(logf logger.Logf, tundev tun.Device, netMon *netmon.Monitor,
+	health *health.Tracker, bus *eventbus.Bus,
+) (Router, error) {
 	logf = logger.WithPrefix(logf, "router: ")
-	return newUserspaceRouter(logf, tundev, netMon, health)
+	return newUserspaceRouter(logf, tundev, netMon, health, bus)
 }
 
 // CleanUp restores the system network configuration to its original state