net/packet, wgengine/{filter,tstun}: add TSMP ping

Fixes #1467

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/message.go

@@ -56,7 +56,8 @@ type FakeExpireAfterArgs struct {
 }
 
 type PingArgs struct {
-	IP string
+	IP      string
+	UseTSMP bool
 }
 
 // Command is a command message that is JSON encoded and sent by a
@@ -174,7 +175,7 @@ func (bs *BackendServer) GotCommand(ctx context.Context, cmd *Command) error {
 		bs.b.RequestEngineStatus()
 		return nil
 	} else if c := cmd.Ping; c != nil {
-		bs.b.Ping(c.IP)
+		bs.b.Ping(c.IP, c.UseTSMP)
 		return nil
 	}
 
@@ -320,8 +321,11 @@ func (bc *BackendClient) FakeExpireAfter(x time.Duration) {
 	bc.send(Command{FakeExpireAfter: &FakeExpireAfterArgs{Duration: x}})
 }
 
-func (bc *BackendClient) Ping(ip string) {
-	bc.send(Command{Ping: &PingArgs{IP: ip}})
+func (bc *BackendClient) Ping(ip string, useTSMP bool) {
+	bc.send(Command{Ping: &PingArgs{
+		IP:      ip,
+		UseTSMP: useTSMP,
+	}})
 }
 
 func (bc *BackendClient) SetWantRunning(v bool) {