linkshell: parse options and open uplink/downlink logfiles
Log packet arrivals and services (used and unused)
timestamp.cc: Normalize timestamps
link_queue.cc: fix bug causing use of earlier PDOs than eligible

Because the LinkQueue only wakes up to use delivery opportunities
when it has queued packets, previously we were allowing newly-arrived
packets to use PDOs that should have expired.
Include queueing delay in log output
link_queue.cc: fix another bug triggering busy wait detection

Make sure conditions match in wait_time() and write_packets() to
guarantee we will write at least one packet.
Add capacity grapher for linkshell
linkshell: Add --once flag to quit after trace is over