fix IP buffer padding check on 64bit (#146)

* fix IP buffer padding check on 64bit

On 64 bit systems, FreeRTOS_IPInit() would assert
ipconfigBUFFER_PADDING was equal to 14 to "make sure there
is enough space in pucEthernetBuffer to store a pointer."

This prevents the driver from requesting additional
padding, so make the assert greater than or equal to 14.

Also use the final ipBUFFER_PADDING value instead of
ipconfigBUFFER_PADDING, which is probably what was
intended?

* Update after comments

Co-authored-by: Thomas Pedersen <[email protected]>
Co-authored-by: Aniruddha Kanhere <[email protected]>

Author: twpedersen

FreeRTOS_IP.c

@@ -1140,7 +1140,10 @@ BaseType_t FreeRTOS_IPInit( const uint8_t ucIPAddress[ ipIP_ADDRESS_LENGTH_BYTES
     {
         /* This is a 64-bit platform, make sure there is enough space in
          * pucEthernetBuffer to store a pointer. */
-        configASSERT( ipconfigBUFFER_PADDING == 14 );
+        configASSERT( ipconfigBUFFER_PADDING >= 14 );
+
+        /* But it must have this strange alignment: */
+        configASSERT( ( ( ( ipconfigBUFFER_PADDING ) + 2 ) % 4 ) == 0 );
     }
 
     /* Check if MTU is big enough. */