op-mode: T5097: show interfaces should reflect cleared counters

[jestabro]

Change Summary

'show interfaces counters' correctly displays counter stats after a call to 'clear interfaces counters', however, 'show interfaces detail' does not. Add missing update to counter stats.

In the rewrite of vyatta-show-interfaces.pl to show_interfaces.py, one update of counters to reflect a call to 'clear counters' was dropped; the mistake persisted in the update of show_interfaces.py to interfaces.py.

Fix is here for 1.4 for interfaces.py.
Fix for 1.3 for show_interface.py is PR:
#1912

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/T5097

Component(s) name

Proposed changes

How to test

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