devlink: Move size validation to core

Currently the size validation is done via a cb, which is unneeded. The
size validation can be moved to core. The next patch will perform cleanup.

Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>