sd-dhcp-client: anonymize DHCPDISCOVER (fixes #13992)

According to RFC7844 section 3 the DHCPDISCOVER message should not contain option 50 («Requested IP Address») when Anonymize is true

src/libsystemd-network/sd-dhcp-client.c

@@ -875,7 +875,9 @@ static int client_send_discover(sd_dhcp_client *client) {
            address be assigned, and may include the ’IP address lease time’
            option to suggest the lease time it would like.
          */
-        if (client->last_addr != INADDR_ANY) {
+        /* RFC7844 section 3:
+           SHOULD NOT contain any other option. */
+        if (!client->anonymize && client->last_addr != INADDR_ANY) {
                 r = dhcp_option_append(&discover->dhcp, optlen, &optoffset, 0,
                                        SD_DHCP_OPTION_REQUESTED_IP_ADDRESS,
                                        4, &client->last_addr);

src/network/networkd-dhcp-server.c

@@ -284,7 +284,7 @@ int dhcp4_server_configure(Link *link) {
 
         r = sd_dhcp_server_set_emit_router(link->dhcp_server, link->network->dhcp_server_emit_router);
         if (r < 0)
-                return log_link_warning_errno(link, r, "Failed to set router emission for DHCP server: %m");
+                return log_link_error_errno(link, r, "Failed to set router emission for DHCP server: %m");
 
         if (link->network->dhcp_server_emit_timezone) {
                 _cleanup_free_ char *buffer = NULL;
@@ -295,7 +295,7 @@ int dhcp4_server_configure(Link *link) {
                 else {
                         r = get_timezone(&buffer);
                         if (r < 0)
-                                return log_warning_errno(r, "Failed to determine timezone: %m");
+                                return log_error_errno(r, "Failed to determine timezone: %m");
 
                         tz = buffer;
                 }
@@ -316,7 +316,7 @@ int dhcp4_server_configure(Link *link) {
         if (!sd_dhcp_server_is_running(link->dhcp_server)) {
                 r = sd_dhcp_server_start(link->dhcp_server);
                 if (r < 0)
-                        return log_link_warning_errno(link, r, "Could not start DHCPv4 server instance: %m");
+                        return log_link_error_errno(link, r, "Could not start DHCPv4 server instance: %m");
         }
 
         return 0;