Previously, when a DHCP address is renewed and if the IPv4ACD for the
address is enabled, the address will never drop the probing flag, thus
the lifetime of the address will never be updated.
This drops NETWORK_CONFIG_STATE_PROBING, and the IPv4ACD status is
managed another bit, Address.acd_bound. And, the flag is updated only
when the IPv4ACD announced the address or detects conflict.
Previously, if IPv4 ACD is enabled on an address, then we first
assign the address, and start sd-ipv4acd daemon for the address.
This is not only RFC incompliant, but also the address is always
dropped, as the daemon always considers the address is conflicted.
This commit makes networkd first starts sd-ipv4acd daemon to probe
the address, and then the address is configured if no conflict is
detected.
Fixes#17235.