lacp: add fallback-timeout configuration to aggregate interfaces

[aamirshah2k]

Change Scope

• This PR adds a fallback-timeout leaf to the openconfig-lacp model under /lacp/interfaces/interface/config/. This leaf specifies the timeout in seconds to wait for LACP PDUs before the interface falls back to a single port active state. This allows for faster or more predictable failover behaviors when LACP negotiation fails
• This change is backwards compatible as it only adds a new optional leaf to the existing model

Platform Implementations

• Arista : Supported via the port-channel lacp fallback timeout <seconds> command in EOS
• Nokia : Supported via the lacp-fallback-timeout <seconds> command in SR Linux
• Cisco : Supported via the bundle lacp-fallback timeout <seconds> command in IOS-XR

Tree View

[Next, cut and paste the relevant portion of the tree with enough context for reviewers to quickly understand the change.]
```diff
 module: openconfig-lacp
   +--rw lacp
      +--rw config
      |  +--rw system-priority?   uint16
      +--ro state
      |  +--ro system-priority?   uint16
      +--rw interfaces
         +--rw interface* [name]
            +--rw name       -> ../config/name
            +--rw config
            |  +--rw name?              oc-if:base-interface-ref
            |  +--rw interval?          lacp-period-type
            |  +--rw lacp-mode?         lacp-activity-type
            |  +--rw system-id-mac?     oc-yang:mac-address
            |  +--rw fallback?          boolean
+           |  +--rw fallback-timeout?   uint16
            |  +--rw system-priority?   uint16
            +--ro state
            |  +--ro name?              oc-if:base-interface-ref
            |  +--ro interval?          lacp-period-type
            |  +--ro lacp-mode?         lacp-activity-type
            |  +--ro system-id-mac?     oc-yang:mac-address
            |  +--ro fallback?          boolean
+           |  +--ro fallback-timeout?   uint16
            |  +--ro system-priority?   uint16
            +--rw members
               +--rw member* [interface]
                  +--rw interface    -> ../config/interface
                  +--rw config
                  |  +--rw interface?       oc-if:base-interface-ref
                  |  +--rw port-priority?   uint16
                  +--ro state
                     +--ro interface?               oc-if:base-interface-ref
                     +--ro port-priority?           uint16
                     +--ro activity?                lacp-activity-type
                     +--ro timeout?                 lacp-timeout-type
                     +--ro synchronization?         lacp-synchronization-type
                     +--ro aggregatable?            boolean
                     +--ro collecting?              boolean
                     +--ro distributing?            boolean
                     +--ro system-id?               oc-yang:mac-address
                     +--ro oper-key?                uint16
                     +--ro partner-id?              oc-yang:mac-address
                     +--ro partner-key?             uint16
                     +--ro port-num?                uint16
                     +--ro partner-port-num?        uint16
                     +--ro partner-port-priority?   uint16
                     +--ro last-change?             oc-types:timeticks64
                     +--ro counters
                        +--ro lacp-in-pkts?               oc-yang:counter64
                        +--ro lacp-out-pkts?              oc-yang:counter64
                        +--ro lacp-rx-errors?             oc-yang:counter64
                        +--ro lacp-tx-errors?             oc-yang:counter64
                        +--ro lacp-unknown-errors?        oc-yang:counter64
                        +--ro lacp-errors?                oc-yang:counter64
                        +--ro lacp-timeout-transitions?   oc-yang:counter64

[gemini-code-assist]

Code Review

This pull request introduces a new 'fallback-timeout' leaf to the LACP statistics grouping in the OpenConfig YANG model. The review identifies that the description string for this new leaf exceeds the 70-character line length limit recommended by the project's style guidelines and provides a corrected suggestion.

[dplore]

/gcbrun

[OpenConfigBot]

No major YANG version changes in commit 370b097

[dplore]

This looks good to me, thank you for providing the implementation references. Scheduled for review in April 14, 2026 OC operators review. I am going to mark this last call now with merge target date of April 14,2026 since this is rather straightforward.

[ElodinLaarz]

/gcbrun

[ElodinLaarz]

Reviewed at OC Operators Meeting April 14th, 2026:

Still need the author to fix the failing CI checks.

The units of uint16 seem okay (vendor max are 300 / 3600 seconds; both of which are smaller than 2^16).

Since fallback already exists, this seems reasonable. Will re-review once the CI checks are passing (@dplore left a comment on how to fix it with OC version update.)

[ElodinLaarz]

/gcbrun

[ElodinLaarz]

/gcbrun