dhcp: dhclient: Allow unqualified fqdn.fqdn for DHCPv6

ISC dhclient will always append the zero label to the fqdn.fqdn option.

The dhcp-options(5) suggest that it's perfectly fine to have an
unqualified name.

"... This can be a fully-qualified domain name, or a single label. ..."

The ISC dhcpd will ignore this trailing zero label and do DDNS
regardless.

https://bugzilla.gnome.org/show_bug.cgi?id=761467

src/dhcp/nm-dhcp-dhclient-utils.c

@@ -168,10 +168,7 @@ add_ip4_config (GString *str, GBytes *client_id, const char *hostname, const cha
 static void
 add_hostname6 (GString *str, const char *hostname)
 {
-	/* dhclient only supports the fqdn.fqdn for DHCPv6 and requires a fully-
-	 * qualified name for this option, so we must require one here too.
-	 */
-	if (hostname && strchr (hostname, '.')) {
+	if (hostname) {
 		g_string_append_printf (str, FQDN_FORMAT "\n", hostname);
 		g_string_append (str,
 		                 "send fqdn.server-update on;\n");

src/dhcp/nm-dhcp-dhclient.c

@@ -203,9 +203,6 @@ merge_dhclient_config (NMDhcpDhclient *self,
 		}
 	}
 
-	if (is_ip6 && hostname && !strchr (hostname, '.'))
-		_LOGW ("hostname is not a FQDN, it will be ignored");
-
 	new = nm_dhcp_dhclient_create_config (iface, is_ip6, client_id, anycast_addr, hostname, fqdn, orig_path, orig, out_new_client_id);
 	g_assert (new);
 	success = g_file_set_contents (conf_file, new, -1, error);

src/dhcp/tests/test-dhcp-dhclient.c

@@ -440,6 +440,9 @@ test_override_hostname6 (void)
 static const char *nonfqdn_hostname6_expected = \
 	"# Created by NetworkManager\n"
 	"\n"
+	"send fqdn.fqdn \"blahblah\"; # added by NetworkManager\n"
+	"send fqdn.server-update on;\n"
+	"\n"
 	"also request dhcp6.name-servers;\n"
 	"also request dhcp6.domain-search;\n"
 	"also request dhcp6.client-id;\n"
@@ -448,7 +451,7 @@ static const char *nonfqdn_hostname6_expected = \
 static void
 test_nonfqdn_hostname6 (void)
 {
-	/* Non-FQDN hostname can't be used with dhclient */
+	/* Non-FQDN hostname can now be used with dhclient */
 	test_config (NULL, nonfqdn_hostname6_expected,
 	             TRUE, "blahblah",
 	             NULL, NULL,