netkvm: Optimize hash calculation when VIRTIO_NET_F_HASH_REPORT is negotiated

[zjmletang]

Background

When VIRTIO_NET_F_HASH_REPORT is negotiated, the driver currently computes its own Toeplitz hash and compares it against the device-reported hash. Based on the presence of framesRSSError counter, this appears to be an intentional verification design, not an oversight:

// Driver always computes hash
ParaNdis6_RSSAnalyzeReceivedPacket(...);

// Then verifies against device-reported hash
if (PacketInfo->RSSHash.Type && pContext->bHashReportedByDevice)
{
    if (val != PacketInfo->RSSHash.Type || ph->hash_value != PacketInfo->RSSHash.Value)
    {
        pContext->extraStatistics.framesRSSError++;  // Intentional verification counter
    }
}

Evidence of Intentional Design

• framesRSSError counter exists specifically to track hash mismatches
• TraceNoPrefix logs the mismatch details for debugging
• The comparison logic is explicit and well-structured

Question

Given that this verification mechanism was intentionally designed (likely for development/validation phase), should we now optimize it for production by directly using device-reported hash when available?