Relax test on overlapping stamps when checking stamp sanity.
Relax test on overlapping stamps when checking stamp sanity.

Now that we allow out of order packets, this test is not relevant anymore.
Changed it into a debug warning, and replace error returning one with something
a bit less strict.
If the NTP client is producing several stamps per-poll period because of
retransmission, each stamp will be passed to the algo.

synclab/radclock,synclab/radclock,synclab/radclock