kernel-doc: strip C99 comments

Strip C99-style comments from the input stream.
/*...*/ comments are already stripped.
C99 comments confuse the kernel-doc script.

Also update some comments.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>