[FS#360] Regression: no ipv6 with multiple interface

[LEDE Bugs]

The following task has a new comment added:

FS#360 - Regression: no ipv6 with multiple interface
User who did this - bastien-roucaries (bastien-roucaries)

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Hi,

As aked during reopen the problem is not the router ipv6 adress but failling to dhcpv6 to affect ipv6 adress.

router adress is like:
26: br-BRIDGE_V20:  mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 14:cc:20:0c:78:5e brd ff:ff:ff:ff:ff:ff
    inet 192.168.20.1/24 brd 192.168.20.255 scope global br-BRIDGE_V20
       valid_lft forever preferred_lft forever
    inet6 fd02:15b3:9237:20::1/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 2a01:e35:2f01:a61::1/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::16cc:20ff:fe0c:785e/64 scope link 
       valid_lft forever preferred_lft forever

client ipv6 are not set ... That is the regression

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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=360#comment1130