添加虚拟串口接收缓存的 ENV 配置项，可手动配置接收缓存大小，默认为128字节

components/drivers/Kconfig

@@ -712,6 +712,9 @@ menu "Using USB"
                     config RT_VCOM_TASK_STK_SIZE
                         int "virtual com thread stack size"
                         default 512
+                    config RT_CDC_RX_BUFSIZE
+                        int "virtual com rx buffer size"
+                        default 128
                     config RT_VCOM_TX_USE_DMA
                         bool "Enable to use dma for vcom tx"
                         default n

components/drivers/usb/usbdevice/class/cdc_vcom.c

@@ -28,7 +28,11 @@
 #define VCOM_TX_TIMEOUT      1000
 #endif /*RT_VCOM_TX_TIMEOUT*/
 
+#ifdef RT_CDC_RX_BUFSIZE
+#define CDC_RX_BUFSIZE          RT_CDC_RX_BUFSIZE
+#else
 #define CDC_RX_BUFSIZE          128
+#endif
 #define CDC_MAX_PACKET_SIZE     64
 #define VCOM_DEVICE             "vcom"