Draft: Fix bad settings for ipv6

With my FAI, i get following during connect to APN

connection error message: IPv6 only allowed

on /etc/NetworkManager/system-connections/*.nmconnection

When i change

[ipv6]
addr-gen-mode=stable-privary
method=ignore

to

[ipv6]
addr-gen-mode=stable-privacy
method=auto

it work well so i think kded/autodetectapn/autodetectapn.cpp not configure well for ipv6 or need to force to automatic mode

I set this MR to ready when i try it on my phone with pmbootstrap