Merge branch 'genetlink-apply-reject-policy-for-split-ops-on-the-dispatch-path'

Jakub Kicinski says:

====================
genetlink: apply reject policy for split ops on the dispatch path

Looks like I somehow missed adding default reject policies to commands
in families using split Netlink ops. I realized this randomly trying
to dump page pools for a specific device and always getting all of them
back. The per-device dump is simply not implemented so the request
should have been rejected. Patch 2 is the real change, the rest is
just accompaniment.
====================

Link: https://patch.msgid.link/20260311032839.417748-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>