let DO_MULTI=1 work for ip6tables* binaries

When defining DO_MULTI=1 in Makefile, only iptables is built as
a single multipurpose binary. This patch makes ip6tables also be
built in the same manner.

Hann-huei Chiou <koala@ascenvision.com>
diff --git a/ip6tables-restore.c b/ip6tables-restore.c
index 8b56c08..f7c3609 100644
--- a/ip6tables-restore.c
+++ b/ip6tables-restore.c
@@ -111,7 +111,11 @@
 		free(newargv[i]);
 }
 
+#ifdef IPTABLES_MULTI
+int ip6tables_restore_main(int argc, char *argv[])
+#else
 int main(int argc, char *argv[])
+#endif
 {
 	ip6tc_handle_t handle = NULL;
 	char buffer[10240];