From Karolis:

Update path of interfaces backup file added by /usr/bin/sosetup-network script 
in the  /etc/network/interfaces file.

from:  /etc/networking/interfaces.bak. to /etc/network/interfaces.bak.

# This configuration was created by the Security Onion setup script.  The 
original network
# interface configuration file was backed up to /etc/networking/interfaces.bak.
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

Done.

Published:
http://blog.securityonion.net/2014/03/new-securityonion-setup-package.html