udhcpc6: set -x options in request

Last foru commits:

function                                             old     new   delta
option_to_env                                        621     791    +170
.rodata                                           168351  168505    +154
attach_option                                        431     506     +75
add_d6_client_options                                112     167     +55
d6_option_strings                                     30      84     +54
udhcp_str2optset                                     644     660     +16
d6_optflags                                           12      20      +8
udhcpc6_main                                        2590    2596      +6
udhcpc_main                                         2648    2651      +3
read_optset                                           15      18      +3
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 10/0 up/down: 544/0)            Total: 544 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index bd9e8fd..c206a58 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -1337,7 +1337,10 @@
 	}
 	while (list_x) {
 		char *optstr = xstrdup(llist_pop(&list_x));
-		udhcp_str2optset(optstr, &client_config.options, dhcp_optflags, dhcp_option_strings);
+		udhcp_str2optset(optstr, &client_config.options,
+				dhcp_optflags, dhcp_option_strings,
+				/*dhcpv6:*/ 0
+		);
 		free(optstr);
 	}