Network-Mode fix

[steiler]

Closes #1939

re-introducing the continue statement for network-namespace sharing, when the referenced namespace is considered an external container. This got messed up via fff2a54#diff-831ecb8143ceda28e72434a64e3b7f88d15f9492071603608fd0180ae3105e67L440-L444

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.66%. Comparing base (e269a28) to head (e3a2171).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1940      +/-   ##
==========================================
+ Coverage   53.53%   53.66%   +0.12%     
==========================================
  Files         155      155              
  Lines       11347    11348       +1     
==========================================
+ Hits         6075     6090      +15     
+ Misses       4413     4403      -10     
+ Partials      859      855       -4     

Files	Coverage Δ
clab/clab.go	75.73% <100.00%> (+0.50%)	⬆️

... and 2 files with indirect coverage changes

[hellt]

ship it @steiler