Merge pull request #15669 from andir/systemd-ipv6-pd-subnet-id

networkd: subnet id support for ipv6 prefix delegation

diff --cc man/systemd.network.xml
Simple merge

diff --cc src/network/networkd-dhcp6.c
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/test/test-socket-util.c
Simple merge

diff --cc test/fuzz/fuzz-network-parser/directives.network
Simple merge