bursty traffic caused when flow count > 1 per port

[mgheorghe]

create a config with many (hundreds or more) flows. mgheorghe/DASH#6
start traffic

observe that all the flows send the traffic in same time, than they wait to meet the flow rate, than again all of them send, then all wait then all send.......
the end result on the wire is a very bursty traffic

burst size is equal with flow no, so 1000 flows we get 1000 packets bursts.
this is very bad for any software solution or emulator, simulator that cannot absorb even 10-100 packet bursts.

we need a port rate option, or a way to delay the streams
or interleave the streams
or anything that can help have a constant packet rate on the wire