main/linux-headers: upgrade to 5.19.4 + bpf backport

So.. This is even worse than I remembered; libbpf is using headers that haven't been merged into mainline linux yet... (the sync target for libbpf is the bpf-next tree, so whatever is in there at the time of the release apparently)

It also includes uapi/linux/netlink.h and other seemingly unrelated headers, but since there are many headers that depend on netlink.h I'm a bit more reluctant to update that one... The no-breakage rule still probably applies but I'm a bit less confident about "files in uapi picked from different kernel versions and mashed together still must work" as being valid.

So unlike what we said to just include their headers in linux-headers I've just backported the required patch, as we're lucky a single one is enough this time. And we'll get the same everytime we upgrade libbpf. Perhaps with 1.0.0 we can try to report it to libbpf upstream and ask if they have any plan for this going forward.

Anyway! With these linux-headers, the check in @acj's MR passes, so all that is left is to make sure we're not breaking too many libbpf users and we can continue that in !38080 (merged)

libbpf 1.0.0 requires bleeding-edge kernel headers (the vendored
linux uapi header they include are not even in mainline linux yet
and come from the bpf-next tree...)

Fortunately we do not need uncommited changes at this point, and
backporting a single patch from the yet-unreleased 6.0 kernel is
enough to use libbpf.

Fixes #14136 (closed)

Cc @acj @psykose