[fix] add input plugin support for v4l2loopback device

Author: wuhanstudio

mjpg-streamer-experimental/plugins/input_uvc/v4l2uvc.h

@@ -41,7 +41,7 @@
 #include <linux/videodev2.h>
 
 #include "../../mjpg_streamer.h"
-#define NB_BUFFER 4
+#define NB_BUFFER 2
 
 
 #define IOCTL_RETRY 4