host_communication: Send zero-length-packet on wMaxPacketSize

We need to send zero-length packets on bulk endpoints whenever the
transfer size is exactly a multiple of the wMaxPacketSize.

See USB 2.0 Specification Section 5.8.3 titled "Bulk Transfer Packet
Size constraints."

Change-Id: Ice3842399d5a5c4a18383860f81074497c6e7c9b
Closes: OS#4331

firmware/atmel_softpack_libraries/usb/include/USBD.h

@@ -214,6 +214,8 @@ typedef void (*MblTransferCallback)(void *pArg,
  *         Exported functions
  *------------------------------------------------------------------------------*/
 
+extern uint16_t USBD_GetEndpointSize(uint8_t bEndpoint);
+
 //extern void USBD_IrqHandler(void);
 
 extern void USBD_Init(void);