fix: regression for docker bridge gw check on darwin dind

[carlmontanari]

little regression after #1482 -- pretty much same issue where clab cant find gw for the bridge (via netlink) and stops even though we have that data from docker inspection.

[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 51.79%. Comparing base (2a5343e) to head (01859ff).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
runtime/docker/docker.go	25.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2364      +/-   ##
==========================================
- Coverage   51.80%   51.79%   -0.01%     
==========================================
  Files         172      172              
  Lines       17240    17243       +3     
==========================================
  Hits         8931     8931              
- Misses       7369     7371       +2     
- Partials      940      941       +1     

Files with missing lines	Coverage Δ
runtime/docker/docker.go	68.67% <25.00%> (-0.26%)	⬇️