This is broken. As soon as you background the openconnect process, there's a race condition where the interface may not be up yet when you attempt to rename it. Having a central script to do half of this stuff goes against the design principles of openconnect. This should be rewritten as a set of hook scripts in /etc/vpnc, particularly the IF renaming chunk.
Or, really, vpnc-script itself should be written to detect the presence of pfSense, and understand that tun devices need to be renamed.