Save the local receive and remote transmit timestamp needed for
(re)starting the symmetric protocol when no valid reply was received
separately from the timestamps that are used for synchronization of the
local clock.
This extends the interval in which the local NTP state is (partially)
protected against replay attacks in order to complete a measurement
in the interleaved symmetric mode from [last valid RX, next TX] to
[last TX, next TX], i.e. it should be the same as in the basic mode.
In interleaved client mode, when so many consecutive requests were lost
that the first valid (interleaved) response would be dropped for being
too old, switch to basic mode so the response can be accepted if it
doesn't fail in the other tests.
This reworks commit 16afa8eb50.
If the -Q option is specified, disable by default pidfile, ntpport,
cmdport, Unix domain command socket, and clock control, in order to
allow starting chronyd without root privileges and/or when another
chronyd instance is already running.
