can: move can_stats.bus_off++ from can_bus_off into can_change_state

In order to be able to move the stats increment from can_bus_off() into
can_change_state(), the increment had to be moved back into code that was using
can_bus_off() but not can_change_state().

As a side-effect, this patch fixes the following bugs:
 * Redundant call to can_bus_off() in c_can.
 * Bus-off counted twice in xilinx_can.

Signed-off-by: Andri Yngvason <andri.yngvason@marel.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>