lib/list_sort: test: use generic random32

Instead of using own pseudo-random generator, use generic linux
'random32()' function.  Presumably, this should improve test coverage.

At the same time, do the following changes:
  o Use shorter macro name for test list length
  o Do not use strange 'l_h' name for 'struct list_head' element,
    use 'list', because it is traditional name and thus, makes the
    code more obvious and readable.

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>