[th/dhcp-acd] dhcp: implement ACD (address collision detection) for DHCPv4
This was working in the past, but broken by l3cfg rework. Re-add it.
Now the NMDhcpClient does ACD (using NML3Cfg) and abstracts that from the caller (NMDevice).
This was working in the past, but broken by l3cfg rework. Re-add it.
Now the NMDhcpClient does ACD (using NML3Cfg) and abstracts that from the caller (NMDevice).