net: mscc: ocelot: select NET_DEVLINK

net: mscc: ocelot: select NET_DEVLINK

Without this option, the driver fails to link:

ld.lld: error: undefined symbol: devlink_sb_register
>>> referenced by ocelot_devlink.c
>>>               net/ethernet/mscc/ocelot_devlink.o:(ocelot_devlink_sb_register) in archive drivers/built-in.a
>>> referenced by ocelot_devlink.c
>>>               net/ethernet/mscc/ocelot_devlink.o:(ocelot_devlink_sb_register) in archive drivers/built-in.a

Fixes: cac31c46b2e4 ("net: mscc: ocelot: configure watermarks using devlink-sb")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20210225143910.3964364-1-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>