[Release 1.34] Fix tailscale setup in case of an already running configuration

[rbrtbnfgl]

Backport #13106
Issue #13217

[codecov]

Codecov Report

❌ Patch coverage is 0% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 21.89%. Comparing base (a9bd7de) to head (799b0d3).

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-1.34   #13267      +/-   ##
================================================
- Coverage         21.91%   21.89%   -0.03%     
================================================
  Files               186      186              
  Lines             15171    15189      +18     
================================================
  Hits               3325     3325              
- Misses            11407    11425      +18     
  Partials            439      439              

Flag	Coverage Δ
unittests	21.89% <0.00%> (-0.03%)	⬇️

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