can: af_can: can_exit(): add missing dev_remove_pack() of canxl_packet

In can_init(), dev_add_pack(&canxl_packet) is added but not removed in
can_exit(). It breaks the packet handler list and can make kernel
panic when can_init() is called for the second time.

| > modprobe can && rmmod can
| > rmmod xxx && modprobe can
|
| BUG: unable to handle page fault for address: fffffbfff807d7f4
| RIP: 0010:dev_add_pack+0x133/0x1f0
| Call Trace:
|  <TASK>
|  can_init+0xaa/0x1000 [can]
|  do_one_initcall+0xd3/0x4e0
|  ...

Fixes: fb08cba1

 ("can: canxl: update CAN infrastructure for CAN XL frames")
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20221031033053.37849-1-chenzhongjin@huawei.com
[mkl: adjust subject and commit message]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>