BPF program should not delete outer map entries in map-in-map

[shpalani]

Describe the bug

Request: ebpf-for-windows should not allow BPF programs to delete outer map entries.

Compatibility with Linux ebpf:
As per Linux doc: https://docs.kernel.org/bpf/map_of_maps.html

• A BPF program cannot update or delete outer map entries.

OS information

Windows 10 and above

Steps taken to reproduce bug

1. Create a map-in-map outer and inner map.
2. In the BPF program, do bpf_map_delete_elem(outer_map, key)

Expected behavior

BPF program should not be allowed to delete the outer map entries, at runtime.

Actual outcome

The outer map entry can be deleted.

Additional details

No response

[shpalani]

The reason I can think of,

1. If an outer map entry is deleted while another part of the program is referencing it, it could lead to undefined behavior or even crashes.

2. Scenario: The User-mode application is the one that does ADD/UPDATE/DELETE of the Maglev map-in-map, and has the state preserved as per the user-supplied configuration. Hence the ebpf program should not delete the entries in the outer-map as it may cause instability.
   For example, in AKS the Load balancer service frontend and backends are configured from the user mode (cni), and the corresponding entries are upserted/deleted in the maglev map-in-map. Let's say, an ebpf program deletes the service id in the outer map, this will cause user-mode application to be out-of-sync with LB service.