net: mvpp2: sync RX data at the hardware packet offset

In the Linux kernel, the following vulnerability has been resolved: net: mvpp2: sync RX data at the hardware packet offset mvpp2 programs the RX queue packet offset, so hardware writes received data at dma_addr + MVPP2_SKB_HEADROOM. The current CPU sync starts at dma_addr and only covers rx_bytes + MVPP2_MH_SIZE bytes, which syncs the unused headroom and misses the same number of bytes at the packet tail. On non-coherent DMA systems this can leave the CPU reading stale cache contents for the end of the received frame. Use dma_sync_single_range_for_cpu() with MVPP2_SKB_HEADROOM as the range offset so the sync covers the Marvell header and packet data actually written by hardware.