ipn/ipnlocal: move handling of expired nodes to LocalBackend

In order to be able to synthesize a new NetMap when a node expires, have
LocalBackend start a timer when receiving a new NetMap that fires
slightly after the next node expires. Additionally, move the logic that
updates expired nodes into LocalBackend so it runs on every netmap
(whether received from controlclient or self-triggered).

Updates #6932

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I833390e16ad188983eac29eb34cc7574f555f2f3

control/controlclient/direct.go

@@ -77,6 +77,7 @@ type Direct struct {
 	popBrowser             func(url string)             // or nil
 	c2nHandler             http.Handler                 // or nil
 	onClientVersion        func(*tailcfg.ClientVersion) // or nil
+	onControlTime          func(time.Time)              // or nil
 
 	dialPlan ControlDialPlanner // can be nil
 
@@ -116,6 +117,7 @@ type Options struct {
 	LinkMonitor          *monitor.Mon                 // optional link monitor
 	PopBrowserURL        func(url string)             // optional func to open browser
 	OnClientVersion      func(*tailcfg.ClientVersion) // optional func to inform GUI of client version status
+	OnControlTime        func(time.Time)              // optional func to notify callers of new time from control
 	Dialer               *tsdial.Dialer               // non-nil
 	C2NHandler           http.Handler                 // or nil
 
@@ -244,6 +246,7 @@ func NewDirect(opts Options) (*Direct, error) {
 		pinger:                 opts.Pinger,
 		popBrowser:             opts.PopBrowserURL,
 		onClientVersion:        opts.OnClientVersion,
+		onControlTime:          opts.OnControlTime,
 		c2nHandler:             opts.C2NHandler,
 		dialer:                 opts.Dialer,
 		dialPlan:               opts.DialPlan,
@@ -1016,6 +1019,9 @@ func (c *Direct) sendMapRequest(ctx context.Context, maxPolls int, readOnly bool
 		}
 		if resp.ControlTime != nil && !resp.ControlTime.IsZero() {
 			c.logf.JSON(1, "controltime", resp.ControlTime.UTC())
+			if c.onControlTime != nil {
+				c.onControlTime(*resp.ControlTime)
+			}
 		}
 		if resp.KeepAlive {
 			vlogf("netmap: got keep-alive")