UNIX and Linux Applications

Hello.
I have an OpenWrt router forwarding traffic from a network to another and I'm building a monitoring tool that requires information about the packet queue/ ring buffer (in the receiving side/interface - rx) occupation, alerting me when it is close to its maximum capacity.

However, after analysing the following files (linux filesystem):

I concluded these files would only be relevant for my program if the router was the destination or source of the TCP packets, which is not the case. So, as I discussed with a professor of mine, the metrics these files provide are not relevant in a forwarding situation, as the packets do not go to the TCP queues.

If that's true, then where (in what folder/file) can I find information about the router's forwarding queue's current occupation and its maximum occupation, if there's any information on the matter? Note that this question is not limited to the OpenWrt OS, but any linux system.

TCP is a "connection-oriented" "end-to-end" client-server protocol.

This means that parameters related to TCP sockets, buffers, lengths, fragments, etc. effect the end-to-end connection and are controlled by the end-to-end TCP connection, not the intermediate routing devices and intermediate hosts.