wgengine/{magicsock,userspace,router}: move portupdates to the eventbus (#17423)

Also pull out interface method only needed in Linux.

Instead of having userspace do the call into the router, just let the
router pick up the change itself.

Updates #15160

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

wgengine/router/router.go

@@ -35,14 +35,6 @@ type Router interface {
 	// implementation should handle gracefully.
 	Set(*Config) error
 
-	// UpdateMagicsockPort tells the OS network stack what port magicsock
-	// is currently listening on, so it can be threaded through firewalls
-	// and such. This is distinct from Set() since magicsock may rebind
-	// ports independently from the Config changing.
-	//
-	// network should be either "udp4" or "udp6".
-	UpdateMagicsockPort(port uint16, network string) error
-
 	// Close closes the router.
 	Close() error
 }
@@ -56,6 +48,14 @@ type NewOpts struct {
 	Bus    *eventbus.Bus   // required
 }
 
+// PortUpdate is an eventbus value, reporting the port and address family
+// magicsock is currently listening on, so it can be threaded through firewalls
+// and such.
+type PortUpdate struct {
+	UDPPort         uint16
+	EndpointNetwork string // either "udp4" or "udp6".
+}
+
 // HookNewUserspaceRouter is the registration point for router implementations
 // to register a constructor for userspace routers. It's meant for implementations
 // in wgengine/router/osrouter.