Implement Dummy Interface

[steiler]

The Linux Dummy interface is the /dev/null of network interfaces.
It can be used if you need a certain amount of interfaces. They can be set to operational up without requiring a peer endpoint.

[hellt]

thanks mate
for context for me when getting to the docs https://developers.redhat.com/blog/2018/10/22/introduction-to-linux-interfaces-for-virtual-networking#dummy

[codecov]

Codecov Report

Attention: Patch coverage is 65.33333% with 26 lines in your changes missing coverage. Please review.

Project coverage is 53.90%. Comparing base (2b735d9) to head (5b70b7b).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2055      +/-   ##
==========================================
+ Coverage   53.82%   53.90%   +0.07%     
==========================================
  Files         160      162       +2     
  Lines       11524    11599      +75     
==========================================
+ Hits         6203     6252      +49     
- Misses       4458     4474      +16     
- Partials      863      873      +10     

Files	Coverage Δ
links/endpoint_raw.go	81.25% <100.00%> (+1.25%)	⬆️
links/link_veth.go	82.45% <ø> (+1.75%)	⬆️
links/endpoint_dummy.go	77.77% <77.77%> (ø)
links/link.go	62.14% <44.44%> (-1.63%)	⬇️
links/link_dummy.go	69.56% <69.56%> (ø)

... and 5 files with indirect coverage changes