[BUG] IPv6 RA does not work on Aruba CX

[ipspace]

Aruba CX either doesn't send IPv6 RA, or sends them too slowly for the adjacent Linux hosts to create the default route.

• Test topology: https://github.com/ipspace/netlab/blob/dev/tests/integration/initial/02-loopback.yml
• Validation results: https://netlab-cicd.pages.dev/arubacx/libvirt/initial/02-loopback.yml-validate.log