lib/Kconfig.debug: add list_sort debugging switch

While hunting a non-existing bug in 'list_sort()', I've improved the
'list_sort_test()' function which tests the 'list_sort()' library call.
Although at the end I found a bug in my code, but not in 'list_sort()', I
think my clean-ups and improvements are worth merging because they make
the test function better.

This patch:

Make the self-tests selectable via Kconfig rather than by manual enabling
of DEBUG_LIST_SORT.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: Don Mullis <don.mullis@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 0d5c762..95bda87 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -748,6 +748,15 @@
 
 	  If unsure, say N.
 
+config TEST_LIST_SORT
+	bool "Linked list sorting test"
+	depends on DEBUG_KERNEL
+	help
+	  Enable this to turn on 'list_sort()' function test. This test is
+	  executed only once during system boot, so affects only boot time.
+
+	  If unsure, say N.
+
 config DEBUG_SG
 	bool "Debug SG table operations"
 	depends on DEBUG_KERNEL