It's a library needed by libnetfilter_queue.
libnetfilter_queue is needed to install python package NetfilterQueue
Yes, as per our submitting a package documentation, patches shouldn't be submitted for applications that aren't accepted for inclusion yet (and since you haven't submitted a package request yet, it hasn't been accepted).
Well, what I need personally is python package NetfilterQueue which provides bindings for libnetfilter_queue and needs libnetfilter_queue to be installed. This package, libnfnetlink, is libnetfilter_queue's dependency, so what I planned was to package it first and then package libnetfilter_queue. Should I change then T5036 to package request for libnetfilter_queue or it's dependency?
No it's fine but I'd suggest building these packages from source using the local repo functionality in solbuild and providing those other packages as patches as well (use Phabricator's stack functionality to create a graph of what depends on what, use "Depends on Dblahblah", where blahblah is the differential number, such as 1309. Once we get those patches, I'll re-review this again and we can see about landing it :)