IPv6: disable accept_ra/autoconf race condition

[karelvanhecke]

Bug Report

Similar issue as #10649.
Most of the time a SLAAC generated IPv6 address is set on a host where a static IPv6 address is configured through NoCloud network config and accepting router advertisements is disabled.

Description

NoCloud network config v2:

version: 2
ethernets:
  eth0:
    accept-ra: false # Likely not respected by talos
    addresses:
      - 2001:db8::3/64
    routes:
      - to: default
        via: 2001:db8::1
    nameservers:
      addresses:
        - 2001:db8::::2

Machine config (likely required do to accept-ra not being respected):

machine:
  sysctls:
    net.ipv6.conf.eth0.accept_ra: "0"
    net.ipv6.conf.eth0.autoconf: "0"

When we check the values set my sysctl, we see that they are applied. Yet the node still has a dynamically configured addresses most of the time.

net.ipv6.conf.eth0.accept_ra = 0
net.ipv6.conf.eth0.autoconf = 0

Environment

• Talos version: v1.13.4
• Kubernetes version: v1.36.1
• Platform: nocloud