How to access conntrack connection expiration in a netfilter module?

[Ed W <lists@wildgooses.com>]

Hi, I'm trying to update the opendpi-netfilter module to work with more 
recent kernels and the ntop ndpi fork of the code (now that opendpi 
seems to have gone away)

The netfilter module registers a conntrack notifier in order to release 
resources once a conntrack is destroyed
https://github.com/ewildgoose/ndpi-netfilter/blob/master/src/main.c
This is not possible though, if you also want to have conntrack events 
through netlink... ( NF_CT_NETLINK grabs the conntrack notifier first)

Now I have read the history on why this is the case, but what are the 
obvious workarounds to this situation?  Can we extend the conntrack 
connection with custom properties? Anything better than simply scanning 
my flows occasionally and comparing with the conntrack list to see if 
they have gone away?

Thanks for any thoughts

Ed W