Enclosed patch fixes inappropriate uses of the .SS macro.  Fuller explanation
in the change comment.

There are other problems in these pages that block lifting to
XML-DocBook, most notably in the command synopses.  They will take
some creativity to fix.  I'm working on it

>From 75745adba4b45b87577b61a2daa886dd444f44da Mon Sep 17 00:00:00 2001
From: "Eric S. Raymond" <esr@thyrsus.com>
Date: Fri, 21 Jun 2013 15:27:38 -0400
Subject: [PATCH] Abolish presentation-level misuse of the .SS macro.

This change fixes most (but not all) fatal errors in attempts to lift
the iproute2 manual pages to XML-DocBook.  Where .SS is still used it
is a real subsection header, not just a way to outdent and bold text.
Presentation-level instances are turned into .TP calls and tables.