Please set the following parameters in configuration file /etc/dpi/fastdpi.conf. You can find more details in option's description "Statistics collection and analysis":

netflow=3
netflow_dev=eth1
netflow_timeout=60
netflow_as_direction=3
netflow_collector=192.168.0.1:9997
netflow_as_collector=192.168.0.1:9998
#Turn on UDP detection
only_tcp=0

Here:
192.168.0.1 - is IP address of a computer with nfsen
eth1 - is the network interface name to export netflow through. (Typically it is the same interface as the control one. DNA interfaces can not be used.)
only_tcp=0 - to switch on UDP protocols detection.