I don't know anything about linux, but it looks like dummynet for
FreeBSD just uses ipfw, the regular firewall utility, so it seems
unlikely to me that dummynet will be able to accomplish anything that
ipfw can't.
So I guess the question is whether ipfw deletes the banned packets
before or after Stefan's user-level tcp sender/receiver copies them
out of the stack. I'm not sufficiently network stack-savvy to figure
that out right now.
Gretta