While this method here is somewhat noisy on the network it eliminates
a poor user experience when the handler is started but the payload is
not yet running on the target.
When a target is sent a udp packet and it is not rejected push down
an initial "echo syn" command that will respond with output. This
allows framework to be aware that the payload is what is running on
the server port instead of assuming a non-existent target is a valid
session.
Jeffrey Martin
f5768e7ced