CAN: add SAE J1939 protocol

This series adds SAE J1939 support to the current net-next-2.6.

1/5: can: extend sockaddr_can to include j1939 members
2/5: can: add rtnetlink support
3/5: j1939: initial import of SAE J1939
4/5: j1939: add documentation & MAINTAINERS
5/5: iproute2: use CAN & J1939

Differences from v3:
* Address claiming does not need a state machine anymore
* Dropped a per-ECU lock.
* Tasklets fill the gap between hrtimer (hardirq context)
  and networking (softirq context), without needing
  spin_lock_irqsave() & friends.
* Added example sendto() code in documentation

Differences from v2:
* replace magic constants with macro's
* use a static protocol stack, not a dynamic one.
* remove feature that have limited use and are
  difficult to explain.
* renamed some structure types to increase code readability.
* block on transport sessions until CAN frame is queued.

Kind regards,
Kurt Van Dijck