[Nexthop][fboss2-dev] Add lookup-class CLI to config/delete interface commands

[vybhav-nexthop]

Summary

This PR adds a new attribute, lookup-class, to the existing fboss2-dev config interface and delete interface command families:

fboss2-dev config interface <interface-name> lookup-class <id>[,<id>...]   # replace the port's lookup-class list
fboss2-dev delete interface <interface-name> lookup-class                  # clear the port's lookup classes

What is a lookup class? Each front-panel port in the agent config carries a list field, Port.lookupClasses (a list<AclLookupClass> in switch_config.thrift). When this list is non-empty, the agent tags every neighbor (host) learned on that port with one of the class IDs from the list, and ACLs then match on those class IDs to steer each host's traffic into a specific egress queue. This is the mechanism behind the "queue-per-host" feature used on multi-host NICs (MH-NIC): several hosts share one physical switch port, and lookup classes let the switch give each host its own queue so one host cannot starve the others.

How the commands behave:

• Set replaces whatever list the port currently has with the given list. Real queue-per-host deployments configure the full class pool (e.g. 10,11,12,13,14) so the agent can spread hosts across five queues; a single id is also accepted.
• Delete resets the list to empty ([]), the field's default ("no per-host classification on this port"). Deleting individual ids from the list is intentionally not supported — clear-all covers the use case; an id-list delete form can be added later if a real need appears.
• Validation: only the queue-per-host classes (CLASS_QUEUE_PER_HOST_QUEUE_0..9, ids 10-19) are accepted — the other AclLookupClass members (CLASS_DROP, DST_CLASS_L3_LOCAL_*, ...) are assigned by the agent itself and are rejected as reserved. Ids and enum names (case-insensitive) are both accepted. Unknown values, duplicate ids, and empty list slots (10,,11) are all rejected; the error lists every valid id and its name.
• No traffic impact when applied (HITLESS): the change is staged in a config session and, on commit, flows through the agent's normal port-settings update path. Verified on hardware: committing reloads the config for fboss_sw_agent without restarting the agents or disrupting the port.

Changed files:

File	Change
commands/config/interface/CmdConfigInterface.cpp	lookup-class attribute; id-list parse/validate (enum check, duplicates, empty slots) + apply
commands/delete/interface/CmdDeleteInterface.{h,cpp}	lookup-class valueless delete attribute (clears lookupClasses)
test/config/CmdConfigInterfaceTest.cpp	13 unit tests (set path: single id, lists, names, error cases)
test/config/CmdDeleteInterfaceTest.cpp	3 unit tests (delete path: clear, idempotent, multi-port)
test/integration_test/ConfigInterfaceLookupClassTest.cpp	7 end-to-end tests, all verifying the running config (4 rejection + 3 commit-path)
cmake/CliFboss2TestIntegrationTest.cmake, test/integration_test/BUCK	wire the new test file into both build systems

Test Plan

• Unit tests: set path (parse, apply single id and comma-separated lists, replacing an existing list, multiple ports, rejecting non-numeric / out-of-range / duplicate / empty-slot input) and delete path (clear all, idempotent when already empty, multiple ports); full cmd_config_test suite run to check for regressions
• Integration tests against a real switch (an NH-4010-F lab device): every test verifies the port's lookupClasses in the agent running config — rejected inputs assert it is unchanged; happy-path tests pick an eth port with an empty lookupClasses baseline, commit the staged change and verify the port's lookupClasses in the agent running config, then delete + commit and verify it clears — the device is restored to its original state; fboss_sw_agent / fboss_hw_agent@0 stayed active through all commits (hitless)

Sample usage, including the committed result in the live agent config:

$ fboss2-dev config interface eth1/1/1 lookup-class 10,11,12,13,14
Successfully configured interface(s) eth1/1/1: lookup-class=10,11,12,13,14
$ fboss2-dev config session commit
Config session committed successfully and config reloaded for fboss_sw_agent.

# /etc/coop/agent.conf now has eth1/1/1 lookupClasses [10, 11, 12, 13, 14]

$ fboss2-dev delete interface eth1/1/1 lookup-class
Successfully reset attribute 'lookup-class' for interface(s): eth1/1/1
$ fboss2-dev config session commit

# eth1/1/1 lookupClasses now [] (back to default)

$ fboss2-dev config interface eth1/1/1 lookup-class 999
Invalid lookup-class value '999'. Valid values: 10 (CLASS_QUEUE_PER_HOST_QUEUE_0),
11 (CLASS_QUEUE_PER_HOST_QUEUE_1), ... 19 (CLASS_QUEUE_PER_HOST_QUEUE_9)

$ fboss2-dev config interface eth1/1/1 lookup-class 9
Invalid lookup-class value '9': CLASS_DROP is reserved for agent use. Valid values: 10 (CLASS_QUEUE_PER_HOST_QUEUE_0), ...

$ fboss2-dev delete interface eth1/1/1 lookup-class 11,13
Unknown delete attribute '11,13'. Valid attributes are: loopback-mode, lookup-class, ...