kmod: bunch of internal functions renames

This patchset does a bunch of cleanups and converts khelper to use system
unbound workqueues.  The 3 first patches should be uncontroversial.  The
last 2 patches are debatable.

Kmod creates kernel threads that perform userspace jobs and we want those
to have a large affinity in order not to contend busy CPUs.  This is
(partly) why we use khelper which has a wide affinity that the kernel
threads it create can inherit from.  Now khelper is a dedicated workqueue
that has singlethread properties which we aren't interested in.

Hence those two debatable changes:

_ We would like to use generic workqueues. System unbound workqueues are
  a very good candidate but they are not wide affine, only node affine.
  Now probably a node is enough to perform many parallel kmod jobs.

_ We would like to remove the wait_for_helper kernel thread (UMH_WAIT_PROC
  handler) to use the workqueue. It means that if the workqueue blocks,
  and no other worker can take pending kmod request, we can be screwed.
  Now if we have 512 threads, this should be enough.

This patch (of 5):

Underscores on function names aren't much verbose to explain the purpose
of a function.  And kmod has interesting such flavours.

Lets rename the following functions:

* __call_usermodehelper -> call_usermodehelper_exec_work
* ____call_usermodehelper -> call_usermodehelper_exec_async
* wait_for_helper -> call_usermodehelper_exec_sync

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>