can: fix build dependency

A recent bugfix introduced a new problem with Kconfig dependencies:

WARNING: unmet direct dependencies detected for CAN_DEV
  Depends on [n]: NETDEVICES [=n] && CAN [=m]
  Selected by [m]:
  - CAN [=m] && NET [=y]

Since the CAN core code now links into the CAN device code, that
particular function needs to be available, though the rest of it
does not.

Revert the incomplete fix and instead use Makefile logic to avoid
the link failure.

Fixes: cb2dc6d286 ("can: Kconfig: select CAN driver infrastructure by default")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512091523.zty3CLmc-lkp@intel.com/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20251204100015.1033688-1-arnd@kernel.org
[mkl: removed module option from CAN_DEV help text (thanks Vincent)]
[mkl: removed '&& CAN' from Kconfig dependency (thanks Vincent)]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/Kconfig

@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
 menuconfig CAN_DEV
-	tristate "CAN Device Drivers"
+	bool "CAN Device Drivers"
 	default y
 	depends on CAN
 	help
@@ -17,9 +17,6 @@ menuconfig CAN_DEV
 	  virtual ones. If you own such devices or plan to use the virtual CAN
 	  interfaces to develop applications, say Y here.
 
-	  To compile as a module, choose M here: the module will be called
-	  can-dev.
-
 if CAN_DEV
 
 config CAN_VCAN

drivers/net/can/Makefile

@@ -7,7 +7,7 @@ obj-$(CONFIG_CAN_VCAN)		+= vcan.o
 obj-$(CONFIG_CAN_VXCAN)		+= vxcan.o
 obj-$(CONFIG_CAN_SLCAN)		+= slcan/
 
-obj-y				+= dev/
+obj-$(CONFIG_CAN_DEV)		+= dev/
 obj-y				+= esd/
 obj-y				+= rcar/
 obj-y				+= rockchip/

drivers/net/can/dev/Makefile

@@ -1,9 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0
 
-obj-$(CONFIG_CAN_DEV) += can-dev.o
-
-can-dev-y += skb.o
+obj-$(CONFIG_CAN) += can-dev.o
 
+can-dev-$(CONFIG_CAN_DEV) += skb.o
 can-dev-$(CONFIG_CAN_CALC_BITTIMING) += calc_bittiming.o
 can-dev-$(CONFIG_CAN_NETLINK) += bittiming.o
 can-dev-$(CONFIG_CAN_NETLINK) += dev.o

net/can/Kconfig

@@ -5,7 +5,6 @@
 
 menuconfig CAN
 	tristate "CAN bus subsystem support"
-	select CAN_DEV
 	help
 	  Controller Area Network (CAN) is a slow (up to 1Mbit/s) serial
 	  communications protocol. Development of the CAN bus started in