Add packetizer_test.mdl

This version is the original implementation that does not have added latency
before and after the mux in the packetizer.
Increase packetizer latency in packetizer_test.mdl

This new implementation still works, but now with more latency in the
packetizer.
Increase latency in the packetizers in sma_corr

This adds a cycle of latency before and after the mux in each of the four
packetizer blocks in sma_corr/netowrk/packetizers.  Same latency change as in
most recent packetizer_test.mdl change.