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/libchip_sam3s/source/USBD_HAL.c

@@ -1077,6 +1077,14 @@ static inline uint8_t UDP_Read(uint8_t  bEndpoint,
  *      Exported functions
  *---------------------------------------------------------------------------*/
 
+
+uint16_t USBD_GetEndpointSize(uint8_t bEndpoint)
+{
+    Endpoint *pEndpoint = &(endpoints[bEndpoint]);
+
+    return pEndpoint->size;
+}
+
 /**
  * USBD (UDP) interrupt handler
  * Manages device resume, suspend, end of bus reset.