docs: pdfdocs: Add space for chapter counts >= 100 in TOC

It turns out that networking.pdf has exceeded 100 chapters and
titles of chapters >= 100 collide with their counts in its table
of contents (TOC).

Increase relevant params by 0.6em in the preamble to avoid such
ugly collisions.

While at it, fix a typo in comment (subsection).

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Link: https://lore.kernel.org/r/bdb60ba3-7813-47d0-74f9-7c31dd912d95@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/sphinx/kerneldoc-preamble.sty

@@ -20,13 +20,13 @@
 %  - Indent of 2 chars is preserved for ease of comparison.
 % Summary of changes from default params:
 %   Width of page number (\@pnumwidth): 1.55em -> 2.7em
-%   Width of chapter number:            1.5em  -> 1.8em
-%   Indent of section number:           1.5em  -> 1.8em
+%   Width of chapter number:            1.5em  -> 2.4em
+%   Indent of section number:           1.5em  -> 2.4em
 %   Width of section number:            2.6em  -> 3.2em
-%   Indent of sebsection number:        4.1em  -> 5em
+%   Indent of subsection number:        4.1em  -> 5.6em
 %   Width of subsection number:         3.5em  -> 4.3em
 %
-% These params can have 4 digit page counts, 2 digit chapter counts,
+% These params can have 4 digit page counts, 3 digit chapter counts,
 % section counts of 4 digits + 1 period (e.g., 18.10), and subsection counts
 % of 5 digits + 2 periods (e.g., 18.7.13).
 \makeatletter
@@ -37,7 +37,7 @@
   \ifnum \c@tocdepth >\m@ne
     \addpenalty{-\@highpenalty}%
     \vskip 1.0em \@plus\p@
-    \setlength\@tempdima{1.8em}%
+    \setlength\@tempdima{2.4em}%
     \begingroup
       \parindent \z@ \rightskip \@pnumwidth
       \parfillskip -\@pnumwidth
@@ -51,8 +51,8 @@
     \endgroup
   \fi}
 %% Redefine \l@section and \l@subsection
-\renewcommand*\l@section{\@dottedtocline{1}{1.8em}{3.2em}}
-\renewcommand*\l@subsection{\@dottedtocline{2}{5em}{4.3em}}
+\renewcommand*\l@section{\@dottedtocline{1}{2.4em}{3.2em}}
+\renewcommand*\l@subsection{\@dottedtocline{2}{5.6em}{4.3em}}
 \makeatother
 %% Sphinx < 1.8 doesn't have \sphinxtableofcontentshook
 \providecommand{\sphinxtableofcontentshook}{}