Merge pull request #22452 from yuwata/network-ipv6ll

network: use sysctl to set IPv6LL address generation mode when the interface is already up

diff --cc src/network/networkd-link.c
Simple merge

diff --cc src/network/networkd-link.h
Simple merge

diff --cc src/network/networkd-network-gperf.gperf
Simple merge

diff --cc src/network/networkd-network.c
Simple merge

diff --cc src/network/networkd-network.h
Simple merge

diff --cc src/network/networkd-setlink.c
Simple merge

diff --cc test/test-network/systemd-networkd-tests.py
Simple merge