kernel-doc: do not warn about duplicate default section names

Since

commit 32217761ee9db0215350dfe1ca4e66f312fb8c54
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Sun May 29 09:40:44 2016 +0300

    kernel-doc: concatenate contents of colliding sections

we started getting (more) errors on duplicate section names, especially
on the default section name "Description":

include/net/mac80211.h:3174: warning: duplicate section name 'Description'

This is usually caused by a slightly unorthodox placement of parameter
descriptions, like in the above case, and kernel-doc resetting back to
the default section more than once within a kernel-doc comment.

Ignore warnings on the duplicate section name automatically assigned by
kernel-doc, and only consider explicitly user assigned duplicate section
names an issue.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>

scripts/kernel-doc

@@ -542,8 +542,11 @@ sub dump_section {
         $new_start_line = 0;
     } else {
 	if (defined($sections{$name}) && ($sections{$name} ne "")) {
-	    print STDERR "${file}:$.: warning: duplicate section name '$name'\n";
-	    ++$warnings;
+	    # Only warn on user specified duplicate section names.
+	    if ($name ne $section_default) {
+		print STDERR "${file}:$.: warning: duplicate section name '$name'\n";
+		++$warnings;
+	    }
 	    $sections{$name} .= $contents;
 	} else {
 	    $sections{$name} = $contents;