ntpd: show real, unclamped delays on low-latency networks

ntpd: show real, unclamped delays on low-latency networks

On fast network, I've seen "delay:0.002000" shown for all packets,
thus completely losing information on what real delays are.

The new code is careful to not reject packets with tiny delays
if the delay "grows a lot" but is still tiny:
0.000009 is "much larger" than 0.000001 (nine times larger),
but is still very good small delay.

function                                             old     new   delta
recv_and_process_peer_pkt                            863     889     +26

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>