wgengine, ipn: include number of active DERPs in status

Use this when making the ipn state transition from Starting to
Running. This way a network of quiet nodes with no active
handshaking will still transition to Active.

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>

ipn/backend.go

@@ -33,6 +33,7 @@ func (s State) String() string {
 type EngineStatus struct {
 	RBytes, WBytes wgengine.ByteCount
 	NumLive        int
+	LiveDERPs      int // number of active DERP connections
 	LivePeers      map[tailcfg.NodeKey]wgengine.PeerStatus
 }
 

ipn/local.go

@@ -520,6 +520,7 @@ func (b *LocalBackend) parseWgStatus(s *wgengine.Status) EngineStatus {
 		RBytes:    rx,
 		WBytes:    tx,
 		NumLive:   live,
+		LiveDERPs: s.DERPs,
 		LivePeers: peers,
 	}
 }
@@ -710,7 +711,7 @@ func (b *LocalBackend) nextState() State {
 		// (if we get here, we know MachineAuthorized == true)
 		return Starting
 	} else if state == Starting {
-		if b.EngineStatus().NumLive > 0 {
+		if st := b.EngineStatus(); st.NumLive > 0 || st.LiveDERPs > 0 {
 			return Running
 		} else {
 			return state