T7066: VPP CPU workers verification

[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/T7066

Related PR(s)

Proposed changes

Added verification for "vpp cpu workers"

How to test

set vpp settings interface eth0 driver dpdk
set vpp settings cpu main-core 0
set vpp settings cpu workers 99

vyos@vyos# commit
[ vpp ]
"cpu workers" cannot be not more than 3
[[vpp]] failed
Commit failed
[edit]

vyos@vyos# set vpp settings cpu workers 3
[edit]
vyos@vyos# commit
[edit]

vyos@vyos# sudo vppctl "show threads"
ID     Name                Type        LWP     Sched Policy (Priority)  lcore  Core   Socket State
0      vpp_main                        3076    other (0)                0      0      0
1      vpp_wk_0            workers     3083    other (0)                1      1      0
2      vpp_wk_1            workers     3084    other (0)                2      2      0
3      vpp_wk_2            workers     3085    other (0)                3      3      0

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

[dmbaturin]

I'd change that wording a bit.

[natali-rs1985]

Added smoke test