Aggregate L3 errors with L2 discards for interfaces with RIF

[stepanblyschak]

Fixes sonic-net/sonic-buildimage#19715

- What I did

Today we sum L2 and L3 errors on RX/TX in ifInErrors/ifOutErrors counters that are part of RFC1213 MIB.
It appears that the monitoring system is using ifInErrors as a way to detect CRC errors on physical interfaces.

The RFC vaguely defines ifInErrors as:

 ifInErrors OBJECT-TYPE
              SYNTAX  Counter
              ACCESS  read-only
              STATUS  mandatory
              DESCRIPTION
                      "The number of inbound packets that contained
                      errors preventing them from being deliverable to a
                      higher-layer protocol."

instead, aggregate errors on L3 as part of ifInDiscard and ifOutDiscard.

- How I did it

Removed aggregation logic and updated UT.

- How to verify it

Manual snmpwalk on interfaces - trigger L3 error - e.g. packet with dst map != router mac, check counter by snmpwalk.

Generate RIF RX errors:

admin@sonic:~$ show interface counters rif
    IFACE    RX_OK    RX_BPS    RX_PPS    RX_ERR    TX_OK    TX_BPS    TX_PPS    TX_ERR
---------  -------  --------  --------  --------  -------  --------  --------  --------
Ethernet0        0  0.00 B/s    0.00/s       100        0  0.00 B/s    0.00/s         0
  Vlan100        1  0.00 B/s    0.00/s         0        0  0.00 B/s    0.00/s         0

Before this change (14 - error, 13 - discard):

admin@sonic:~$ docker exec -it snmp snmpwalk -v2c -c public localhost 1.3.6.1.2.1.2.2.1.14.1
iso.3.6.1.2.1.2.2.1.14.1 = Counter32: 100
admin@sonic:~$ docker exec -it snmp snmpwalk -v2c -c public localhost 1.3.6.1.2.1.2.2.1.13.1
iso.3.6.1.2.1.2.2.1.13.1 = Counter32: 0

After this change:

admin@sonic:~$ docker exec -it snmp snmpwalk -v2c -c public localhost 1.3.6.1.2.1.2.2.1.14.1
iso.3.6.1.2.1.2.2.1.14.1 = Counter32: 0
admin@sonic:~$ docker exec -it snmp snmpwalk -v2c -c public localhost 1.3.6.1.2.1.2.2.1.13.1
iso.3.6.1.2.1.2.2.1.13.1 = Counter32: 100

- Description for the changelog

[stepanblyschak]

@bingwang-ms @SuvarnaMeenakshi Please review

[SuvarnaMeenakshi]

@stepanblyschak thank you for fixing this.
Per discussion, can we have RIF errors included as a part of ifInDiscards/ifOutDiscards instead completely removing it from being aggregated. Currently it is aggregated as a part of ifInError/ifOutErrors
RIF counters are not supported on all hwsku. On the hwskus that do not support them, a packet with a RIF error is dropped and counted as part of the discard counter.

[stepanblyschak]

@SuvarnaMeenakshi ifInDiscard is port buffer drops. Do we know that no monitor app is treating ifInDiscard as port buffer drops? As we are talking about breaking change for established release, a simple revert is less destructive than remap.

[stepanblyschak]

@SuvarnaMeenakshi Discussed offline, your comment is addressed, please review

[SuvarnaMeenakshi]

lgtm

[mssonicbld]

Cherry-pick PR to 202405: #326

[bingwang-ms]

@yxieca Can you please approve the cherry-pick to 202311 branch? Thanks

[mssonicbld]

Cherry-pick PR to 202311: #327