[BUG] IPv6 RA missing on RouterOS7

[ipspace]

Mikrotik RouterOS7 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/01-interfaces.yml
• Validation results: https://netlab-cicd.pages.dev/routeros7/libvirt/initial/01-interfaces.yml-validate.log