[Nexthop] Clear egress queue stats for all port queues, not just the configured…

[vvasavada-nexthop]

… ones

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Summary

Root cause

clear interface counters reported success but left per-interface Output Discards unchanged, while Input Discards on the same port cleared correctly.

SaiPortManager::clearStats clears the port level counters and then the egress queue drop counters, but it only walked portHandle->configuredQueues. That list is built from the SwtichState port queue config, and BroadcomXgsAsic::getQueueStreamTypes(INTERFACE_PORT) returns {UNICAST} - so the multicast queues, which exist in HW and are present in SAI's QOS_QUEUE_LIST (and therefore in portHandle->queues), were never in it.

On XGS the port level SAI_PORT_STAT_IF_OUT_DISCARDS is derived from the sum of the per queue drop counters across every queue, so any queue left out of the clear pins HwPortStats::outDiscards_ at a non-zero value indefinitely. Drops parked on multicast queue - flooded BUM traffic, e.g. a port that is the sole member of its VLAN - therefore survived the clear.

Input Discards was unaffected before inDiscards_ is accumulated in software and explicitly zeroed in clearStats, which masks the same behavior on the ingress size.

Fix

Iterate portHandle->queues instead.

Test Plan

Before fix

  # fboss2 show interface errors
   Interface Name  Input Errors  Input Discards  Output Errors  Output Discards
  ------------------------------------------------------------------------------------
   eth1/18/1       0             1               0              24096

  # fboss2 clear interface counters
  Counters cleared.

  # sleep 15   (allow a counter refresh interval)
  # fboss2 show interface errors
   Interface Name  Input Errors  Input Discards  Output Errors  Output Discards
  ------------------------------------------------------------------------------------
   eth1/18/1       0             0               0              24096

After fix

  # fboss2 show interface errors
   Interface Name  Input Errors  Input Discards  Output Errors  Output Discards
  ------------------------------------------------------------------------------------
   eth1/18/1       0             0               0              48621

  # fboss2 clear interface counters
  Counters cleared.

  # sleep 15   (allow a counter refresh interval)
  # fboss2 show interface errors
   Interface Name  Input Errors  Input Discards  Output Errors  Output Discards
  ------------------------------------------------------------------------------------
   eth1/18/1       0             0               0              0