Simple networking test stuff, to compare splice/vmsplice with
send()/recv(). The basic setup is transmitting and receiving
buffers of data with crc checksums attached. Speed and sys/usr
stats are shown, so both performance and data integrity can
be tested.

The basic pair is xmit/recv, which talk to each other. It's
important to use the same message size, or it wont work. sf can
also talk to recv. To do that, you need to prepare a data file
with fillfile first.