[intelxl] Add missing padding bytes to receive queue context

For the sake of completeness, ensure that all 32 bytes of the receive
queue context are programmed (including the unused final 8 bytes).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/intelxl.h

@@ -685,6 +685,8 @@ struct intelxl_context_rx {
 	uint8_t reserved_b[7];
 	/** Maximum frame size */
 	uint16_t mfs;
+	/** Reserved */
+	uint8_t reserved_c[8];
 } __attribute__ (( packed ));
 
 /** Receive queue base address and queue count */