Fix Network-interface of the Xilinx UltraScale port (#588)

The underlying issue was when the port would be used with Jumbo frames.
During receives of Jumbo packets the data length was always set
incorrectly, which then would cause buffer allocation issues and
subsequently corrupted data would be sent to the IP-task.

After some inspection in the Xilinx UltraScale port, I found out
that when the data length would be set, the wrong mask from the
Xilinx Ethernet MAC driver would be used. By using the right mask
(XEMACPS_RXBUF_LEN_JUMBO_MASK) when Jumbo Frame support is enabled
the issue was resolved

Author: ChristosZosi

source/portable/NetworkInterface/xilinx_ultrascale/x_emacpsif_dma.c

@@ -79,13 +79,13 @@
 #if ( ipconfigNETWORK_MTU > 1526 )
     #warning the use of Jumbo Frames has not been tested sufficiently yet.
     #define USE_JUMBO_FRAMES    1
-#endif
+#endif /* ( ipconfigNETWORK_MTU > 1526 ) */
 
 #if ( USE_JUMBO_FRAMES == 1 )
     #define dmaRX_TX_BUFFER_SIZE    10240
 #else
     #define dmaRX_TX_BUFFER_SIZE    1536
-#endif
+#endif /* ( USE_JUMBO_FRAMES == 1 ) */
 
 #if ( ipconfigULTRASCALE == 1 )
     extern XScuGic xInterruptController;
@@ -430,8 +430,19 @@ int emacps_check_rx( xemacpsif_s * xemacpsif )
 
             /*
              * Adjust the buffer size to the actual number of bytes received.
+             * If port is built with Jumbo Frame support, then the XEMACPS_RXBUF_LEN_JUMBO_MASK
+             * should be used to obtain the size of the buffer. Otherwise the mask
+             * XEMACPS_RXBUF_LEN_MASK can be used.
              */
-            rx_bytes = xemacpsif->rxSegments[ head ].flags & XEMACPS_RXBUF_LEN_MASK;
+            #if ( USE_JUMBO_FRAMES == 1 )
+                {
+                    rx_bytes = xemacpsif->rxSegments[ head ].flags & XEMACPS_RXBUF_LEN_JUMBO_MASK;
+                }
+            #else
+                {
+                    rx_bytes = xemacpsif->rxSegments[ head ].flags & XEMACPS_RXBUF_LEN_MASK;
+                }
+            #endif /* ( USE_JUMBO_FRAMES == 1 ) */
 
             pxBuffer->xDataLength = rx_bytes;