net: mscc: ocelot: select PACKING in the Kconfig

Ocelot now uses include/linux/dsa/ocelot.h which makes use of
CONFIG_PACKING to pack/unpack bits into the Injection/Extraction Frame
Headers. So it needs to explicitly select it, otherwise there might be
build errors due to the missing dependency.

Fixes: 40d3f295b5fe ("net: mscc: ocelot: use common tag parsing code with DSA")
Reported-by: Naresh Kamboju <[e-mail]>
Signed-off-by: Vladimir Oltean <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/mscc/Kconfig

···
 # Users should depend on NET_SWITCHDEV, HAS_IOMEM
 config MSCC_OCELOT_SWITCH_LIB
 	select REGMAP_MMIO
+	select PACKING
 	select PHYLIB
 	tristate
 	help