Kernel prepatch 6.0-rc4

The 6.0-rc4 kernel prepatch is out for
testing. 'We're up to rc4, and things mostly still look fairly
normal'.

Beyond the usual fixes, 6.0-rc4 includes one feature change: a hook to allow
security modules to control access to the io_uring command pass-through
mechanism. See this article for the
background behind this late-arriving change.