dns scavenging: tombstone deletion uses correct time units

dns scavenging: tombstone deletion uses correct time units

Before we were comparing hours to 1e-7 second units.

Now we do it both ways. That's because in dns_tombstone_records (in
this same file) we have been putting hour timestamps in EntombedTime,
but this field is supposed to have NTTIME timestamps, and those
timestamps won't have updated themselves.

This wouldn't matter much in pure Samba networks if we weren't also
using the correct timestamp in dns_common_replace().

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>