ntpd: drop delay outliers; run "unsync" handler if no replies for some time

function                                             old     new   delta
ntpd_main                                            960    1029     +69
recv_and_process_peer_pkt                            834     892     +58
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(add/remove: 0/0 grow/shrink: 2/0 up/down: 127/0)             Total: 127 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Merge git://busybox.net/busybox