kho/abi: memfd: make generated documentation more coherent

kho/abi: memfd: make generated documentation more coherent

memfd preservation ABI description starts with "This header defines" which
is fine in the header but reads weird in the generated html documentation.

Update it to make the generated documentation coherent.

Link: https://lkml.kernel.org/r/20260105165839.285270-3-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Jason Miu <jasonmiu@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>