[PATCH] DocBook/HTML: Generate chapter/section level TOCs for functions

Simple increase of section TOC level generation significantly enhances
navigation experience through generated kernel API documentation.

This change restores back state from SGML tools time.

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>