[gen] ipv6: fix network_adapter select + add code to fail on unhandled cases

5 jobs for ipv6 in 4 minutes and 43 seconds (queued for 20 seconds)
Status Name Job ID Coverage
  Validate
passed rubocop #599586
grid5000-docker

00:00:52

passed validate-data #599587
grid5000-docker

00:01:54

 
  Generate
passed generate-reference-api #599588
grid5000-docker

00:01:18

 
  Deploy
passed deploy #599589
grid5000-shell

00:00:08

passed rspec #599590
grid5000-docker

00:01:25