wgengine/router: add debug logging component logs

This uses the "component logging" feature to allow turning on additional
debug logs for the Router at runtime. Currently, it's only implemented
on Linux and with the CallbackRouter at this time.

Updates #13887

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I251a7705765f950d118850f1e14f465729ba45c5

ipn/ipnlocal/local.go

@@ -566,7 +566,9 @@ func componentStateKey(component string) ipn.StateKey {
 // The following components are recognized:
 //
 //   - magicsock
+//   - router
 //   - sockstats
+//   - syspolicy
 func (b *LocalBackend) SetComponentDebugLogging(component string, until time.Time) error {
 	b.mu.Lock()
 	defer b.mu.Unlock()
@@ -575,6 +577,12 @@ func (b *LocalBackend) SetComponentDebugLogging(component string, until time.Tim
 	switch component {
 	case "magicsock":
 		setEnabled = b.MagicConn().SetDebugLoggingEnabled
+	case "router":
+		if r, ok := b.sys.Router.GetOK(); ok {
+			setEnabled = r.SetDebugLoggingEnabled
+		} else {
+			return fmt.Errorf("no router available")
+		}
 	case "sockstats":
 		if b.sockstatLogger != nil {
 			setEnabled = func(v bool) {