Ignore DNS queries with RRs

DNS queries with optional records (RRs), for example, with
cookies for EDNS, are not supported by the OVN resolver.
Trying to reply sometimes results in mangled responses
that clients do not understand.

Instead, just return early when one is present, which
should trigger a negative response and cause clients to
go to the upstream forwarder, hopefully resulting in a
successful query.

Closes issue ovn-org#192
Signed-off-by: Brian Haley <haleyb.dev@gmail.com>

controller/pinctrl.c

@@ -2864,6 +2864,13 @@ pinctrl_handle_dns_lookup(
         goto exit;
     }
 
+    /* Check if there is an additional record present, which is unsupported */
+    if (in_dns_header->arcount) {
+        VLOG_DBG_RL(&rl, "Received DNS query with additional records, which"
+                    " is unsupported");
+        goto exit;
+    }
+
     struct udp_header *in_udp = dp_packet_l4(pkt_in);
     size_t udp_len = ntohs(in_udp->udp_len);
     size_t l4_len = dp_packet_l4_size(pkt_in);