Return link-local address when we are only requesting IPv6 prefix only if there is no global IPv6 address. In some cases global SLAAC IPv6 address might be present when using DHCPv6. Fixes #4483
Related issues
Bug #4483: SLAAC and stateful DHCP6 IPs are configured on interface when using DHCP6 config type
Return link-local address when we are only requesting IPv6 prefix only if there is no global IPv6 address. In some cases global SLAAC IPv6 address might be present when using DHCPv6. Fixes #4483