devlink: Constify the 'table_ops' parameter of devl_dpipe_table_register()

"struct devlink_dpipe_table_ops" only contains some function pointers.

Update "struct devlink_dpipe_table" and the 'table_ops' parameter of
devl_dpipe_table_register() so that structures in drivers can be
constified.

Constifying these structures will move some data to a read-only section, so
increase overall security.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>