tello: send Land() command to drone on Halt() to avoid floating mid-air

Signed-off-by: Ron Evans <[email protected]>

platforms/dji/tello/driver.go

@@ -285,6 +285,11 @@ func (d *Driver) Start() error {
 
 // Halt stops the driver.
 func (d *Driver) Halt() (err error) {
+	// send a landing command when we disconnect, and give it 500ms to be received before we shutdown
+	d.Land()
+	time.Sleep(500 * time.Millisecond)
+
+	// TODO: cleanly shutdown the goroutines that are handling the UDP connections before closing
 	d.cmdConn.Close()
 	d.videoConn.Close()
 	return