network: reset 'configured' flags even if we keep DHCP lease and friends on reconfigure

Follow-up for 451c2baf30.

With the commits, reloading .network files does not release previously
acquired DHCP lease and friends if possible. If previously a DHCP client
was configured as not requesting DNS servers or so, then the previously
acquired lease might not contain any DNS servers. In that case, if the
new .network file enables UseDNS=, then the interface should enter the
configured state after a new lease is acquired. To achieve that, we need
to reset the flags.

With this change, the workaround applied to the test by the commit
451c2baf30 can be dropped.

src/network/networkd-link.c

@@ -1136,6 +1136,15 @@ static int link_drop_dynamic_config(Link *link, Network *network) {
         link->lldp_rx = sd_lldp_rx_unref(link->lldp_rx); /* TODO: keep the received neighbors. */
         link->lldp_tx = sd_lldp_tx_unref(link->lldp_tx);
 
+        /* Even if we do not release DHCP lease or so, reset 'configured' flags. Otherwise, e.g. if
+         * previously UseDNS= was disabled but is now enabled, link will enter configured state before
+         * expected DNS servers being acquired. */
+        link->ipv4ll_address_configured = false;
+        link->dhcp4_configured = false;
+        link->dhcp6_configured = false;
+        link->dhcp_pd_configured = false;
+        link->ndisc_configured = false;
+
         return r;
 }
 

test/test-network/systemd-networkd-tests.py

@@ -6705,7 +6705,6 @@ class NetworkdDHCPClientTests(unittest.TestCase, Utilities):
                       '--dhcp-option=option6:ntp-server,[2600::ff]')
 
         networkctl_reload()
-        networkctl_reconfigure('veth99') # Release previously acquired lease and start new DHCPv6 handshake.
         self.wait_online('veth99:routable', 'veth-peer:routable')
 
         # checking address