[Link Event Damping] Add RedisInterface plumbing for damping config

[DendroLabs]

Summary

Supersedes #1331, originally authored by @Ashish1805. The original PR has been inactive for ~2 years and has merge conflicts against current master.

This PR adds the Redis communication layer for link event damping configuration:

lib/ (orchagent -> Redis):

• sairediscommon.h: New command strings link_event_damping_config_set / link_event_damping_config_response
• RedisRemoteSaiInterface: New isRedisPortAttribute() (port analog to isRedisAttribute()), setRedisPortExtensionAttribute() dispatch, and setLinkEventDampingConfig() which is always synchronous (per @kcudnik review)
• ClientSai::set(): Blocks port extension attrs in CLIENT mode
• Sai::set(): Routes port extension attrs directly, bypassing metadata validation

syncd/ (Redis -> syncd handler):

• Syncd: Dispatches link_event_damping_config_set to processLinkEventDampingConfigSet() stub
• sendLinkEventDampingConfigResponse() always sends a response (no m_enableSyncMode guard), since the lib always waits

Fixes from @kcudnik's review of #1331

1. Always synchronous: setLinkEventDampingConfig unconditionally calls m_communicationChannel->wait(). The original code skipped the wait in async mode, which @kcudnik said was wrong: "make this api always synchronous, async mode is just for create/remove/set operations all other apis should be synchronous."

2. Simplified isRedisPortAttribute: Single boolean expression using reversed condition, per @kcudnik: "you can turn this to 1 single line by reversing condition."

3. Syncd always sends response: sendLinkEventDampingConfigResponse omits the m_enableSyncMode guard, since the lib side always waits unconditionally.

Relation to other PRs

This is part of the Link Event Damping feature:

• [Link Event Damping] Add SelectablesTracker for timer management #1798 (SelectablesTracker) -- merged
• This PR -- Redis plumbing (stub syncd handler)
• [Link Event Damping] Add per port link event damper class. #1334 supersede -- will fill in processLinkEventDampingConfigSet with actual damping algorithm (next)

Test plan

• 3 new unit tests in unittest/lib/TestClientServerSai.cpp (client mode rejection, null pointer rejection, invalid attribute rejection)
• 2 new integration tests in syncd/tests/TestSyncdLinkEventDamping.cpp (full lib->Redis->syncd round trip for algorithm and AIED config, asserting NOT_IMPLEMENTED response from stub)
• Existing tests unaffected -- normal port set operations (speed, MTU, admin state) have attr IDs far below SAI_PORT_ATTR_CUSTOM_RANGE_START (0x10000000)

Credits: Original implementation by @Ashish1805 (PR #1331).

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[DendroLabs]

@kcudnik @mikeberesford — this is the second PR in the link event damping series, following #1798 (SelectablesTracker, merged last week). It adds the Redis communication plumbing, superseding #1331.

All three review comments from #1331 are addressed — the key fix is making the damping config API always synchronous, matching the pattern used by flushFdbEntries and other non-QUAD APIs.

Would appreciate your review when you get a chance. The next PR (#1334 supersede, the actual damping algorithm) depends on this one.

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[prsunny]

@DendroLabs , please review this PR - #1906. You can close #1935 in favor of 1906

[DendroLabs]

Closing in favor of #1906 per @prsunny's suggestion. @sivat6's PR covers this scope and more (full Syncd wiring + damping algorithm + stats).

Our #1798 (SelectablesTracker) is already merged and provides the foundation both approaches build on. Happy to help review #1906 and get it across the finish line — we've done extensive testing of the damping algorithm and can offer some findings.

The CLI (sonic-net/sonic-utilities#4367) and YANG model (sonic-net/sonic-buildimage#26231) PRs remain open as they're independent of the sairedis implementation approach.