Use DS records as trust anchors, not DNSKEYs.

This allows us to query for the root zone DNSKEY RRset and validate
it, thus automatically handling KSK rollover.
diff --git a/src/dnsmasq.c b/src/dnsmasq.c
index 6c19c05..3c8a847 100644
--- a/src/dnsmasq.c
+++ b/src/dnsmasq.c
@@ -144,7 +144,7 @@
   if (option_bool(OPT_DNSSEC_VALID))
     {
 #ifdef HAVE_DNSSEC
-      if (!daemon->dnskeys)
+      if (!daemon->ds)
 	die(_("No trust anchors provided for DNSSEC"), NULL, EC_BADCONF);
       
       if (daemon->cachesize < CACHESIZ)