Kernel prepatch 5.15-rc1

Linus has released 5.15-rc1 and closed the
merge window for this development cycle.

So 5.15 isn't shaping up to be a particularly large release, at
least in number of commits. At only just over 10k non-merge
commits, this is in fact the smallest rc1 we have had in the 5.x
series. We're usually hovering in the 12-14k commit range.

That said, counting commits isn't necessarily the best measure, and
that might be particularly true this time around. We have a few new
subsystems, with NTFSv3 and ksmbd standing out.