docs: security-bugs: clarify what counts as a valid version

docs: security-bugs: clarify what counts as a valid version

Too often we're getting reports saying "still valid in latest mainline"
with no indication of when this was verified, making this indication
pointless. Let's clarify it and insist on having a version or commit ID,
and that the version must necessarily be for a kernel.org kernel and not
a distro one.

Cc: Greg KH <greg@kroah.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Link: https://patch.msgid.link/20260802203540.3453-4-w@1wt.eu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>