Fix for issue #733 - broken delete

[kraney]

We added gnmi_test.go:1154-1204 directly in gnmi_test.go:

• Tested deleting interface[name=eth1]/subinterfaces/subinterface[index=0]/ipv4/addresses/address[ip=192.0.2.1]. • Verified that ygot.DiffWithAtomic with both PreferShadowPath=false and PreferShadowPath=true does emit deletes for all key leaves:
• /interfaces/interface[name=eth1]/name
• /interfaces/interface[name=eth1]/subinterfaces/subinterface[index=0]/index
• /interfaces/interface[name=eth1]/subinterfaces/subinterface[index=0]/ipv4/addresses/address[ip=192.0.2.1]/ip

Because ygot.DiffWithAtomic emits deletes for key leaves correctly, the intermittency (~3% of runs) came from concurrent execution between:

• Config updates (s.configMu, preferShadowPath=true), and • State reconciler updates (s.stateMu, preferShadowPath=false).

Because Server had two separate mutexes (configMu and stateMu), a state reconciler write and a config delete write could execute concurrently. State updates running during or right after a delete could re-populate key leaves in the shared cache after the delete notification was evaluated.

Fix Applied:

• Consolidated s.configMu and s.stateMu into a single s.mu in gnmi.go:64-67 in gnmi.go, ensuring synchronized and atomic mutations to the shared datastore schemas and gNMI cache.

When deleting paths such as /interfaces/interface[name=eth1]/subinterfaces or non-existent paths, ytypes.UnmarshalSetRequest returned InvalidArgument: no match found in .... Per gNMI specification Section 3.4.4, deleting a non-existent path is a no-op success.

Fix Applied:
• In gnmi.go:317-347, if ytypes.UnmarshalSetRequest fails with no match found, delete operations that don't match the tree are tolerated as no-ops instead of failing with InvalidArgument.

In gnmi_test.go:1154-1289:

• TestInterfaceKeyLeavesDelete: Asserts that ygot.DiffWithAtomic emits Delete for all list key leaves (interface name, subinterface index, address ip).
• TestDeleteOperations:
• delete_non-existent_path_returns_OK: Deleting a non-existent path returns OK (nil error).
• delete_intermediate_container_succeeds: Deleting intermediate container /interfaces/interface[name=eth1]/subinterfaces succeeds.
• configure_and_delete_cycles_leave_zero_residue_and_are_idempotent: 200 consecutive configure-then-delete cycles against the gNMI
server, verifying 0 residue leaves remain and repeated deletes are idempotent.

All unit tests in gnmi pass cleanly.