Add route lookup ingress drop counter to interface and subinterface counters

[ostromart]

This change introduces a new operational state counter in-route-lookup-drop under common interface counters (/interfaces/interface/state/counters/in-route-lookup-drop and /interfaces/interface/subinterfaces/subinterface/state/counters/in-route-lookup-drop) to track inbound packets dropped during routing table lookup. This could be due to no matching route entry in the forwarding table (LPM miss) or matching an explicit drop route.
The version has been bumped to 3.11.0 in openconfig-interfaces.yang.

Change-Id: I2f1a6c4290871e86b3e94a815a1e2f89104b28cd

Change Scope

• Description: This PR introduces in-route-lookup-drop to openconfig-interfaces.yang (under interface-common-counters-state) to count inbound packets discarded on a routed interface or subinterface when a routing table lookup fails to find a matching route entry (LPM miss) or encounters an explicit drop/blackhole route.
• Backwards Compatibility: This change is fully backward compatible as it only adds a new read-only operational state leaf counter to the existing interface-common-counters-state grouping.

Use case

In routed fabrics (such as spine-leaf or multi-tenant networks), silent packet discards due to routing table misses or blackhole routes are difficult to isolate using generic discard counters (in-discards). Providing an explicit counter for route lookup drops (in-route-lookup-drop) enables network operations and automated failure pinpointing tools to immediately identify routing blackholes, unassigned IP prefix drops, or route table sync issues at both interface and subinterface granularity.

Platform Implementations

• SAI Specification: Defines explicit debug drop reasons for LPM miss and LPM drops: SAI_IN_DROP_REASON_LPM_MISS / SAI_IN_DROP_REASON_LPM_DROP (SAI Debug Counters Proposal).
• Google Switch Telemetry: Google production switches export granular ingress routing lookup drop telemetry via UMF and SAI debug counters.
• Cisco IOS-XE / NX-OS: Exposes routing drop statistics (ipInputNoRoute / show ip traffic no route discards).
• Arista EOS: Tracks IpNoRoute discards (show ip traffic).
• SONiC / Broadcom Telemetry: Pipeline counters support tracking SWITCH_INGRESS_DROPS with drop reason SAI_IN_DROP_REASON_LPM4_MISS and SAI_IN_DROP_REASON_LPM6_MISS.

Tree View

 module: openconfig-interfaces
   +--rw interfaces
      +--rw interface* [name]
         ...
         +--ro state
         |  +--ro counters
         |     +--ro out-discards?            oc-yang:counter64
         |     +--ro out-errors?              oc-yang:counter64
         |     +--ro last-clear?              oc-types:timeticks64
+        |     +--ro in-route-lookup-drop?    oc-yang:counter64
         ...
         +--rw subinterfaces
            +--rw subinterface* [index]
               ...
               +--ro state
                  +--ro counters
                     +--ro out-discards?           oc-yang:counter64
                     +--ro out-errors?             oc-yang:counter64
                     +--ro last-clear?             oc-types:timeticks64
+                    +--ro in-route-lookup-drop?   oc-yang:counter64

[gemini-code-assist]

Code Review

This pull request updates the openconfig-interfaces YANG module to version 3.11.0, introducing a new 'in-route-lookup-drop' counter leaf. The review feedback highlights two main issues: first, a revision entry for version 3.9.0 is added but the corresponding 'ingress low-TTL discard counter' is missing from the code changes; second, the description for the 3.11.0 revision should be updated to clarify that the new counter applies to both interface and subinterface counters.

[ostromart]

This PR is intended to merge after #1528 and the version reflects that.