Is it platform specific

generic

Importance or Severity

High

Description of the bug

generic_config_updater/test_lo_interface.py was recently updated to run on T2 chassis in #17293
test_lo_interface.py::test_lo_interface_tc1_suite tries to remove all the configured loopback interfaces in cleanup_lo_interface_config.
On T2 chassis this will be 2 loopback ports:

(Pdb) cfg_facts.get('LOOPBACK_INTERFACE',{})
{'Loopback0': {'10.1.0.1/32': {}, 'fc00:10::1/128': {}}, 'Loopback4096': {'2603:10e2:400::1/128': {}, '8.0.0.1/32': {}}}

The problem is if you try to delete Loopback4096 it will return an error:

> sudo config loopback del Loopback4096
Usage: config loopback del [OPTIONS] <loopback_name>
Try 'config loopback del -h' for help.

Error: Loopback4096 is invalid, name should have prefix 'Loopback' and suffix '<0-999>'

This upper bound restriction of 999 comes from this code and has been there for a long time:
https://github.com/sonic-net/sonic-utilities/blob/202511/config/main.py#L108

The usage of Loopback4096 comes from the TestbedProcessing script and has been there for a long time as well:
https://github.com/sonic-net/sonic-mgmt/blob/master/ansible/TestbedProcessing.py#L713-L717

Steps to Reproduce

Run generic_config_updater/test_lo_interface.py on T2.

Actual Behavior and Expected Behavior

generic_config_updater/test_lo_interface.py should pass on T2.

Relevant log output

Output of show version

Attach files (if any)

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