T6497: CGNAT refactoring delete conntrack entries (backport #3699)

[mergify]

Change Summary

Refactoring of the deleting conntrack entries.
Use native ipaddress.summary function
Delete only required entries by internal network

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

Related PR(s)

Component(s) name

cgnat

Proposed changes

How to test

Smoketest result

vyos@r4:~$ /usr/libexec/vyos/tests/smoke/cli/test_cgnat.py
test_cgnat (__main__.TestCGNAT.test_cgnat) ... 
Rule must be defined!


Rule must be defined!


External pool "fake-pool" does not exist!

ok
test_cgnat_sequence (__main__.TestCGNAT.test_cgnat_sequence) ... ok

----------------------------------------------------------------------
Ran 2 tests in 24.286s

OK
vyos@r4:~$ 

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

---

This is an automatic backport of pull request #3699 done by [Mergify](https://mergify.com).

[github-actions]

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