network: fix DHCPv4 address renewal with IPv4ACD

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.

src/network/networkd-ipv4acd.h

@@ -5,6 +5,7 @@ typedef struct Address Address;
 typedef struct Link Link;
 
 bool link_ipv4acd_supported(Link *link);
+bool ipv4acd_bound(const Address *address);
 int ipv4acd_configure(Address *address);
 int ipv4acd_update_mac(Link *link);
 int ipv4acd_start(Link *link);