T7069: VPP check for CPU main core

[natali-rs1985]

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)
• Other (please describe):

Related Task(s)

• https://vyos.dev/T7069

Related PR(s)

Proposed changes

How to test

vyos@vyos# lscpu | grep -i on-line
On-line CPU(s) list:                  0-4

set vpp settings cpu main-core 99

vyos@vyos# commit
[ vpp ]
"cpu main-core 99" is not available!
[[vpp]] failed
Commit failed
[edit]

Checklist:

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