Disable container IPv6 SLAAC addressing

[diasdmhub]

I have an AdGuard Home v0.107.53 instance running as a container and pointing to an Unbound instance.

AdGuard uses a static IPv6 local address and Unbound has an ACL to allow AdGuard's queries.
However, AdGuard is also getting a SLAAC IPv6 from my network. So it ends up with 3 IPv6 addresses, like this:

# ip add show eth0
    inet 192.168.8.5/24 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fd01:192:168:8:ecb2:17ff:fe94:cbd7/64 scope global dynamic flags 100   ## unecessary
       valid_lft 2591960sec preferred_lft 604760sec
    inet6 fd01:192:168:8::5/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::ecb2:17ff:fe94:cbd7/64 scope link 
       valid_lft forever preferred_lft forever

Whenever the container is rebooted, AdGuard gets a different IPv6 from router advertisements.
I would like to disable this IPv6 addressing based on router advertisements, and keep only the static one, but could not find such a configuration. Or, maybe, set the out interface address AdGuard should use.

Any suggestions?