Exporting Priority Flow Control (PFC) counters

[Peter Phaal]

The following proposal defines a structure for periodically exporting a set of PFC counters along with standard interface counters.

https://sflow.org/draft_sflow_pfc.txt

Supporting PFC-specific counters within the sFlow protocol is critical for maintaining high-performance, lossless Ethernet environments, such as those used for AI/ML training and RoCEv2 (RDMA over Converged Ethernet). Important use cases for reporting PFC counters in sFlow include: * Reveal "silent" congestion due to paused links * Visibility into network deadlocks due to PFC storms * Correlate traffic and drops with flow control

Please review and comment.