net/can: simple messages transport implementation for QEMU

net/can: simple messages transport implementation for QEMU

The CanBusState state structure is created for each
emulated CAN channel. Individual clients/emulated
CAN interfaces or host interface connection registers
to the bus by CanBusClientState structure.

The CAN core is prepared to support connection to the
real host CAN bus network. The commit with such support
for Linux SocketCAN follows.

Implementation is as simple as possible.  There is no state to be
migrated, and messages prioritization and queuing are not considered
for now.  But it is intended to be extended when need arises.

Development repository and more documentation at

https://gitlab.fel.cvut.cz/canbus/qemu-canbus

The work is based on Jin Yang GSoC 2013 work funded
by Google and mentored in frame of RTEMS project GSoC
slot donated to QEMU.

Rewritten for QEMU-2.0+ versions and architecture cleanup
by Pavel Pisa (Czech Technical University in Prague).

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>