nat66: T6365: remove warnings for negated interface selections by name (backport #3505)

[mergify]

Change Summary

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)

• https://vyos.dev/T6365

Related PR(s)

• nat: T6365: remove warnings for negated interface selections by name #3482

Component(s) name

NAT66

Proposed changes

Filter leading ! character

How to test

Smoketest result

cpo@LR1.wue3:~$ /usr/libexec/vyos/tests/smoke/cli/test_nat66.py
test_destination_nat66 (__main__.TestNAT66.test_destination_nat66) ... ok
test_destination_nat66_prefix (__main__.TestNAT66.test_destination_nat66_prefix) ... ok
test_destination_nat66_protocol (__main__.TestNAT66.test_destination_nat66_protocol) ... ok
test_destination_nat66_without_translation_address (__main__.TestNAT66.test_destination_nat66_without_translation_address) ... ok
test_nat66_no_rules (__main__.TestNAT66.test_nat66_no_rules) ... ok
test_source_nat66 (__main__.TestNAT66.test_source_nat66) ... ok
test_source_nat66_address (__main__.TestNAT66.test_source_nat66_address) ... ok
test_source_nat66_protocol (__main__.TestNAT66.test_source_nat66_protocol) ... ok
test_source_nat66_required_translation_prefix (__main__.TestNAT66.test_source_nat66_required_translation_prefix) ... ok

----------------------------------------------------------------------
Ran 9 tests in 28.527s

OK

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

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This is an automatic backport of pull request #3505 done by [Mergify](https://mergify.com).