net: Always descend into dsa/

Jiri reported that with a kernel built with CONFIG_FIXED_PHY=y,
CONFIG_NET_DSA=m and CONFIG_NET_DSA_LOOP=m, we would not get to a
functional state where the mock-up driver is registered. Turns out that
we are not descending into drivers/net/dsa/ unconditionally, and we
won't be able to link-in dsa_loop_bdinfo.o which does the actual mock-up
mdio device registration.

Reported-by: Jiri Pirko <[e-mail]>
Fixes: 40013ff20b1b ("net: dsa: Fix functional dsa-loop dependency on FIXED_PHY")
Signed-off-by: Florian Fainelli <[e-mail]>
Reviewed-by: Vivien Didelot <[e-mail]>
Tested-by: Jiri Pirko <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/Makefile

···
 obj-$(CONFIG_DEV_APPLETALK) += appletalk/
 obj-$(CONFIG_CAIF) += caif/
 obj-$(CONFIG_CAN) += can/
-obj-$(CONFIG_NET_DSA) += dsa/
+obj-y += dsa/
 obj-$(CONFIG_ETHERNET) += ethernet/
 obj-$(CONFIG_FDDI) += fddi/
 obj-$(CONFIG_HIPPI) += hippi/