Draft: selection: balance the choice of IPv4/IPv6 servers when RTT cache is clear

On clear RTT and in the presence of miscunfigured IP protocol version (e.g. net.ipv6 enabled but IPv6 doesn't work), resolver might waste a lot of time and packets trying to query nameservers using the broken protocol.

We choose the protocol first and if there is some candidate server with unknown RTT and using the chosen protocol, we swap it to the front and it is used for the transport.

If there is none, tough luck, we still want to try all the candidates before going back trying some again.

daemon/worker.c

@@ -1361,7 +1361,7 @@ static int udp_task_step(struct qr_task *task,
 	/* Announce and start subrequest.
 	 * @note Only UDP can lead I/O as it doesn't touch 'task->pktbuf' for reassembly.
 	 */
-	subreq_lead(task);
+	// subreq_lead(task);
 
 	return kr_ok();
 }