can: rename LED trigger name on netdev renames

The LED trigger name for CAN devices is based on the initial
CAN device name, but does never change. The LED trigger name
is not guaranteed to be unique in case of hotplugging CAN devices.

This patch tries to address this problem by modifying the
LED trigger name according to the CAN device name when
the latter changes.

v1 - Kurt Van Dijck
v2 - Fabio Baltieri
- remove rename blocking if trigger is bound
- use led-subsystem function for the actual rename (still WiP)
- call init/exit functions from dev.c
v3 - Kurt Van Dijck
- safe operation for non-candev based devices (vcan, slcan)
	based on earlier patch
v4 - Kurt Van Dijck
- trivial patch mistakes fixed

Signed-off-by: Kurt Van Dijck <kurt.van.dijck@eia.be>
Signed-off-by: Fabio Baltieri <fabio.baltieri@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>