ntpd: be less eager to use shorter poll intervals

* on step, poll interval drops to 8.5 mins instead of 32 seconds
* on total loss of all replies (no replies from any peer
  for last 8 requests), also drop poll interval to 8.5 mins
  instead of 32 seconds
* on send abd recv errors, RETRY_INTERVAL is now 32 seconds,
  not 5 seconds
* on timing out listening to reply, instead of unconditional
  shortening poll interval by x4, clamp it to NOREPLY_INTERVAL
  (512 seconds)
* if a largish offset is seen, clamp nexp poll interval
  to 128 seconds, not 64 seconds

function                                             old     new   delta
clamp_pollexp_and_set_MAXSTRAT                         -      37     +37
recv_and_process_peer_pkt                            861     869      +8
poll_interval                                         52      48      -4
update_local_clock                                   762     752     -10
ntpd_main                                           1063    1050     -13
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/3 up/down: 45/-27)             Total: 18 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
getty: set tty attrs so that control chars are shown as ^c

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
ntpd: don't stay at short polling interval

To avoid polling servers frequently slowly increase the interval up
to BIGPOLL when
- no replies are received from a peer
- no source can be selected
- peer claims to be unsynchronized (e.g. we are polling it too
  frequently)

When recv() returns with an error, drop code to try to continue
on network errors: I'm not convinced those cases happen in real life.

function                                             old     new   delta
recv_and_process_peer_pkt                            919     838     -81

Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
sed: fix "sed CMD -i nonexistent_file". Closes 7484

function                                             old     new   delta
sed_main                                             643     676     +33

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
ntpd: calculate offset to jitter ratio before updating jitter

The offset to jitter ratio is now calculated before updating
jitter to make the test more sensitive.

function                                             old     new   delta
ntp_init                                             460     474     +14
update_local_clock                                   752     764     +12
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 26/0)               Total: 26 bytes

Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>