net: l3mdev: use obj-$(CONFIG_NET_L3_MASTER_DEV) form in net/Makefile

CONFIG_NET_L3_MASTER_DEV is a bool option. Change the ifeq conditional
to the standard obj-$(CONFIG_NET_L3_MASTER_DEV) form.

Use obj-y in net/l3mdev/Makefile because Kbuild visits this Makefile
only when CONFIG_NET_L3_MASTER_DEV=y.

Signed-off-by: Masahiro Yamada <[e-mail]>
Reviewed-by: David Ahern <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/Makefile

···
 obj-$(CONFIG_NET_NSH)		+= nsh/
 obj-$(CONFIG_HSR)		+= hsr/
 obj-$(CONFIG_NET_SWITCHDEV)	+= switchdev/
-ifneq ($(CONFIG_NET_L3_MASTER_DEV),)
-obj-y				+= l3mdev/
-endif
+obj-$(CONFIG_NET_L3_MASTER_DEV)	+= l3mdev/
 obj-$(CONFIG_QRTR)		+= qrtr/
 obj-$(CONFIG_NET_NCSI)		+= ncsi/
 obj-$(CONFIG_XDP_SOCKETS)	+= xdp/

net/l3mdev/Makefile

···
 # Makefile for the L3 device API
 #
 
-obj-$(CONFIG_NET_L3_MASTER_DEV) += l3mdev.o
+obj-y += l3mdev.o