RoCEv2: Add DCQCN congestion control

[ruck314]

Summary

Adds DCQCN (Data Center Quantized Congestion Notification) congestion control to the RoCEv2 engine, plus the supporting IPv4/UDP and AXI-Stream changes needed to carry ECN/CNP signaling.

Originally developed on FilMarini/surf:dcqcnEn; migrated here and merged up to current pre-release (conflict-free).

Changes

DCQCN core (new modules under ethernet/RoCEv2/rtl/)

• Dcqcn.vhd, AlphaUpdate.vhd, RateIncProc.vhd, RateDecProc.vhd — rate control state machine
• TokenBucket.vhd, AxisBucket.vhd, TokenCalc.vhd — token-bucket rate limiter
• AxiStreamMonDcqcn.vhd — rate/throughput monitoring
• RoceEngineWrapper.vhd — wiring + Dcqcn_en enable parameter; CNP output port

ECN/CNP signaling path

• IpV4Engine.vhd / IpV4EngineTx.vhd — DSCP + ECN fields in the IPv4 header
• EthMacRxRoCEv2.vhd, RocePkg.vhd, UdpEngineWrapper.vhd — plumbing
• Sgmii88E1111LvdsUltraScale.vhd — RoceV2_en parameter for the RJ45 PHY path

blue-rdma regen — mkQP.v, mkAxisTransportLayer.v, mkTransportLayer.v (QP destroy fix, RNR-retry-with-fragmentation fix, full 2-byte address, sequential pipeline for timing)

AXI-Stream — AxiStreamCompact.vhd reworked for the congestion-control data path

Software — python/surf/ethernet/roce/_RoceEngine.py DCQCN RemoteVariable register map

Review notes

• AxiStreamCompact.vhd is a full rewrite of an existing shared surf module (not a new file). This is the main item to scrutinize — confirm it preserves behavior for existing non-DCQCN users.
• DCQCN is gated behind the Dcqcn_en generic; default-off behavior should be confirmed.

Status

Draft — pending FW review and register cross-check.