It stopped working when ntp_packetstamp.c was split out
of ntp_io.c.  USE_PACKET_TIMESTAMP was defined in ntp_packetstamp.c
but referenced in ntp_io.c.

All modern systems support some form of capturing recv
time stamps via recvmsg.  The current code is using a time
stamp from shortly after the select returns.  We can restore
that action if necessary.  It seems to work OK on lightly
loaded systems.  (Very old code used SIGIO to capture
time stamps.)

It will crash if it can't use one of:
  SO_BINTIME, SO_TIMESTAMPNS,or SO_TIMESTAMP
It will crash if recvmsg doesn't get the expected timestamp data.
Hack around SO_BINTIME on FreeBSD not working with IPv6.