[Release 1.31] Fix tailscale setup in case of an already running configuration

[rbrtbnfgl]

Backport #13106
Issue #13220

[codecov]

Codecov Report

❌ Patch coverage is 0% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 21.02%. Comparing base (ccf884b) to head (9937dac).
⚠️ Report is 1 commits behind head on release-1.31.

Files with missing lines	Patch %	Lines
pkg/vpn/vpn.go	0.00%	15 Missing ⚠️
pkg/agent/flannel/setup.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.31   #13270      +/-   ##
================================================
- Coverage         21.04%   21.02%   -0.03%     
================================================
  Files               189      189              
  Lines             15548    15566      +18     
================================================
  Hits               3272     3272              
- Misses            11829    11847      +18     
  Partials            447      447              

Flag	Coverage Δ
unittests	21.02% <0.00%> (-0.03%)	⬇️

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