Support nanosecond-resolution time stamp adjustment.

Based on https://code.wireshark.org/review/#/c/4304/ from Peter Hatina.

Change-Id: Ibc5e230b0682990fd4ca1f29597a9a045cb73928
Reviewed-on: https://code.wireshark.org/review/4356
Reviewed-by: Guy Harris <guy@alum.mit.edu>