passes in parameters for the rest of loss and bw.

----

not too convinced that poisson is correct (see corresponding dummynet
commit msg)

the command line reading code has ballooned and could use cleaning in some
way. since this is user code, i'm not _terribly_ concerned, but...

should add more to 'ipfw pipe show'.

more validity checking would be nice, but having the kernel catch it and
 give a printf() and EINVAL is not bad.