ionic: select CONFIG_NET_DEVLINK

When no other driver selects the devlink library code, ionic
produces a link failure:

drivers/net/ethernet/pensando/ionic/ionic_devlink.o: In function `ionic_devlink_alloc':
ionic_devlink.c:(.text+0xd): undefined reference to `devlink_alloc'
drivers/net/ethernet/pensando/ionic/ionic_devlink.o: In function `ionic_devlink_register':
ionic_devlink.c:(.text+0x71): undefined reference to `devlink_register'

Add the same 'select' statement that the other drivers use here.

Fixes: fbfb8031 ("ionic: Add hardware init and device commands")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>