STM32H legacy driver fix: request usable RX size in legacy zero-copy path

The STM32H legacy zero-copy RX path still requested ETH_RX_BUF_SIZE for
replacement RX buffers even though BufferAllocation_1 now limits allocations
to the interface-reported usable size.

For this driver the usable size is ETH_RX_BUF_SIZE - ipBUFFER_PADDING.
Requesting the full hardware buffer size caused every replacement allocation
to fail, left pxReceivedBuffer as NULL, and dropped all received frames
before they reached the IP task.

Request ETH_RX_BUF_SIZE - ipBUFFER_PADDING in the RX fast path so the
receive path matches the enforced allocation limit.

Author: liteStefanoUgolini

source/portable/NetworkInterface/STM32/Legacy/STM32Hxx/NetworkInterface.c

@@ -780,8 +780,9 @@ static BaseType_t prvNetworkInterfaceInput( void )
 
         #if ( ipconfigZERO_COPY_RX_DRIVER != 0 )
         {
-            /* Reserve the maximum length for the next reception. */
-            uxLength = ETH_RX_BUF_SIZE;
+            /* Request the usable Ethernet payload area, excluding the descriptor
+             * metadata stored in front of pucEthernetBuffer. */
+            uxLength = ETH_RX_BUF_SIZE - ipBUFFER_PADDING;
 
             if( data_buffer.buffer != NULL )
             {