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: NPavel Pisa <pisa@cmp.felk.cvut.cz>
Acked-by: NRandy Dunlap <rdunlap@xenotime.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>