sendmsg testcase for ded34e0fe8fe8c2d595bfa30626654e4b87621e0

reproducer for:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000250

fixed in 3.9.0-0.rc5:
  commit ded34e0fe8fe8c2d595bfa30626654e4b87621e0
  Author: Paul Moore <pmoore@redhat.com>
  Date:   Mon Mar 25 03:18:33 2013 +0000
    unix: fix a race condition in unix_release()

This reproducer should be able to trigger it easily on 4+ CPU systems
just within couple of seconds.

Signed-off-by: Jan Stancek <jstancek@redhat.com>