In the dec.2009 rewrite I introduced a bug, using for the
computation the arrival time instead of the time the packet
has exited from the queue.
The bandwidth computation was still correct because it is
computed elsewhere, but traffic was sent out in bursts.
The bug is also present in RELENG_8 after dec.2009
Thanks to Daikichi Osuga for investingating, finding and fixing the
bug with detailed graphs of the behaviour before and after the fix.
Submitted by: Daikichi Osuga
MFC after: 2 weeks